8
O
Oxygen

Oxygen

Element 8 • Nonmetal
Atomic Mass 15.999000
Electron Config [He] 2s² 2p⁴
Group/Period 16/2

Overview

ANALYZED

The Breath of Life

Oxygen is the third most abundant element in the universe and the most abundant element in Earth's crust, comprising about 21% of our atmosphere and nearly 50% of the planet's mass. This highly reactive, colorless, and odorless gas is absolutely essential for most life forms on Earth through the process of cellular respiration.

Discovered independently by Carl Wilhelm Scheele and Joseph Priestley in the 1770s, Oxygen revolutionized our understanding of combustion and respiration. Its name, derived from the Greek words "oxys" (acid) and "genes" (producer), reflects Antoine Lavoisier's mistaken belief that all acids contained Oxygen.

Fun Fact: The Oxygen we breathe today was largely produced by ancient cyanobacteria through photosynthesis over billions of years, fundamentally changing Earth's atmosphere and enabling complex life to evolve.

Oxygen exists in several allotropes, with dioxygen (O₂) being the form we breathe, and ozone (O₃) forming the protective layer in our stratosphere. In industry, Oxygen supports combustion processes, steel production, and serves as an oxidizing agent in countless chemical reactions.

From the water we drink (H₂O) to the minerals in Earth's crust, Oxygen forms compounds with virtually every other element, making it fundamental to chemistry, biology, and geology. Its unique electronic configuration gives Oxygen its characteristic reactivity and ability to form double bonds, crucial for organic chemistry and life processes.

Physical Properties

MEASURED
Atomic Mass
15.999000 u
Density
0.0014 g/cm³
Melting Point
54.36 °C
Boiling Point
90.20 °C
Electronegativity
3.44
Electron Configuration
[He] 2s² 2p⁴
Ionization Energy
13.62 kJ/mol

Special Properties

CLASSIFIED
STABLE Generally safe to handle with standard precautions
Earth Abundance: 4.61e-1
Universe Abundance: 1.04e-2

Applications

CATALOGUED

Industrial Applications and Manufacturing

Steel and Metal Production

The largest industrial use of Oxygen is in steel manufacturing, where it dramatically improves efficiency and quality:

  • Basic Oxygen Furnace (BOF) - Pure Oxygen is blown through molten iron to remove carbon, producing high-quality steel in 30-40 minutes instead of hours
  • Electric Arc Furnace (EAF) - Oxygen injection increases melting rates and improves energy efficiency in recycling steel scrap
  • Cutting and welding - Oxy-acetylene and oxy-fuel torches reach temperatures over 3,500°C for precise metal cutting
  • Copper smelting - Oxygen enrichment reduces fuel consumption and increases production rates
  • Aluminum production - Oxygen helps remove impurities during aluminum refining processes

Chemical Manufacturing and Processing

Oxygen serves as a critical oxidizing agent in numerous industrial processes:

  • Ethylene oxide production - Direct oxidation of ethylene produces this key chemical intermediate for antifreeze and plastics
  • Vinyl chloride synthesis - Oxygen-based processes create the precursor for PVC plastic production
  • Propylene oxide manufacturing - Essential for producing polyurethane foams and propylene glycol
  • Titanium dioxide production - Oxygen helps create the white pigment used in paints, plastics, and paper
  • Hydrogen peroxide synthesis - Anthraquinone process uses Oxygen to produce this versatile oxidizing agent

Pulp and Paper Industry

Oxygen revolutionized paper manufacturing through environmentally friendly bleaching:

  • Oxygen delignification - Removes lignin from wood pulp without chlorine compounds
  • Ozone bleaching - Generates bright white paper with minimal environmental impact
  • Hydrogen peroxide bleaching - Oxygen-based bleaching creates high-quality recycled paper
  • Biological treatment - Oxygen enhances bacterial breakdown of organic pollutants in paper mill wastewater

Wastewater Treatment and Environmental Applications

Oxygen-based technologies clean water and reduce pollution:

  • Activated sludge process - Aerobic bacteria use Oxygen to break down organic pollutants
  • Ozonation - Ozone (O₃) destroys bacteria, viruses, and organic contaminants
  • Advanced oxidation processes - Hydroxyl radicals generated from Oxygen compounds eliminate persistent pollutants
  • Groundwater remediation - Oxygen injection stimulates biodegradation of soil contaminants
  • Aquaculture - Oxygen injection maintains fish health in intensive farming operations

Aerospace and Rocket Propulsion

Liquid Oxygen (LOX) is the most widely used rocket oxidizer:

  • Space Shuttle program - LOX and liquid hydrogen powered the main engines
  • SpaceX Falcon rockets - Use RP-1 fuel with liquid Oxygen oxidizer
  • Blue Origin - BE-4 engines burn methane with liquid Oxygen
  • Life support systems - Oxygen generation and recycling for spacecraft and space stations
  • Hypersonic flight - Scramjet engines use atmospheric Oxygen for high-speed propulsion

Glass Manufacturing

Oxygen combustion improves glass production efficiency and quality:

  • Oxy-fuel furnaces - Pure Oxygen combustion reaches higher temperatures with less fuel
  • Reduced emissions - Lower NOx production compared to air-fuel combustion
  • Improved glass quality - Higher temperatures enable better melting and homogenization
  • Energy efficiency - 15-50% reduction in fuel consumption compared to conventional furnaces

Common Uses

INDEXED

Medical and Healthcare Applications

Medical Oxygen Therapy

  • Respiratory therapy - Treating pneumonia, COPD, asthma, and COVID-19 patients
  • Emergency medicine - First-line treatment for shock, cardiac arrest, and severe trauma
  • Anesthesia - Carrier gas for inhaled anesthetics during surgery
  • Premature infant care - Carefully controlled Oxygen levels in neonatal intensive care units
  • Home Oxygen therapy - Portable concentrators for patients with chronic respiratory conditions
  • Hyperbaric Oxygen therapy - High-pressure Oxygen treatment for carbon monoxide poisoning and wound healing

Everyday Consumer Applications

  • Drinking water treatment - Ozonation purifies municipal water supplies worldwide
  • Swimming pool sanitation - Ozone generators provide chemical-free water disinfection
  • Air purification - Ozone generators eliminate odors in cars, homes, and hotels
  • Food preservation - Modified atmosphere packaging extends shelf life of fresh produce
  • Aquarium maintenance - Oxygen pumps and aerators maintain fish health
  • Wine production - Micro-oxygenation improves wine flavor and aging characteristics

Automotive and Transportation

  • Oxygen sensors - Lambda sensors optimize air-fuel ratios in modern engines
  • Catalytic converters - Use Oxygen to reduce harmful emissions from vehicles
  • Emergency Oxygen systems - Aircraft passenger Oxygen masks for cabin depressurization
  • Automotive welding - Oxy-acetylene welding for vehicle repair and restoration
  • Racing applications - Nitrous oxide (N₂O) systems inject Oxygen for engine power enhancement

Sports and Fitness

  • Athletic performance - Oxygen bars and canned Oxygen for perceived performance enhancement
  • High-altitude training - Supplemental Oxygen for acclimatization to thin air
  • Diving applications - Nitrox (Oxygen-enriched air) extends underwater time limits
  • Recovery therapy - Post-exercise Oxygen therapy claimed to reduce fatigue
  • Mountain climbing - Supplemental Oxygen for extreme altitude expeditions

Beauty and Wellness

  • Oxygen facials - Spa treatments claiming to rejuvenate skin appearance
  • Oxygen therapy centers - Wellness facilities offering concentrated Oxygen breathing
  • Hair care products - Hydrogen peroxide for hair bleaching and coloring
  • Teeth whitening - Hydrogen peroxide-based whitening treatments
  • Wound care - Hydrogen peroxide for cleaning minor cuts and scrapes

Art and Crafts

  • Glassblowing - Oxygen torches for shaping and manipulating glass
  • Jewelry making - Oxy-propane torches for soldering precious metals
  • Metal sculpture - Cutting and shaping steel and other metals
  • Pottery glazing - Oxidation atmospheres create specific glaze colors and effects
  • Blacksmithing - Oxygen injection into forges for higher temperatures

Scientific and Educational

  • Laboratory experiments - Studying combustion, oxidation, and cellular respiration
  • School demonstrations - Classic experiments showing Oxygen's properties
  • Research applications - Controlled atmosphere chambers for biological studies
  • Analytical chemistry - Combustion analysis for determining organic compound composition
  • Environmental monitoring - Dissolved Oxygen measurements in water quality testing

Natural Occurrence

SURVEYED

Universal Abundance and Natural Sources

Cosmic and Stellar Origin

Oxygen is the third most abundant element in the universe, comprising approximately 1% of all atoms. It is primarily formed through stellar nucleosynthesis in massive stars:

  • Alpha process - Silicon burning in stars produces Oxygen through fusion reactions
  • Helium burning - Triple-alpha process in red giant stars creates carbon, which fuses with helium to form Oxygen
  • Supernova nucleosynthesis -
    Explosive stellar death disperses Oxygen throughout galaxies
  • Stellar winds - Evolved stars continuously enrich interstellar medium with Oxygen

The Oxygen in our solar system formed approximately 4.

6 billion years ago from the gravitational collapse of an Oxygen-rich molecular cloud.

Atmospheric Abundance

Earth's atmosphere contains 20.946% Oxygen by volume, representing the second most abundant atmospheric gas after nitrogen. This massive reservoir contains approximately 1.2 × 10¹⁵ tons of Oxygen gas.

Amazing Fact: Virtually all atmospheric Oxygen is biogenic - produced by photosynthetic organisms over billions of years. The Great Oxidation Event 2.4 billion years ago fundamentally changed Earth's atmosphere.

The atmospheric Oxygen cycle involves constant exchange between:

  • Photosynthesis - Plants, algae, and cyanobacteria produce ~330 billion tons of O₂ annually
  • Respiration - Living organisms consume Oxygen for cellular energy production
  • Combustion - Natural and human-caused fires consume atmospheric Oxygen
  • Chemical weathering - Rock oxidation slowly removes Oxygen from the atmosphere

Crustal and Lithospheric Abundance

Oxygen dominates Earth's crust, comprising approximately 46.1% by weight - making it the most abundant element in the solid Earth. Major Oxygen-bearing minerals include:

Silicate Minerals (95% of crust)
  • Quartz (SiO₂) - Pure silicon dioxide, abundant in sandstone and granite
  • Feldspar group - Potassium, sodium, and calcium aluminosilicates
  • Pyroxene and amphibole - Iron, magnesium, and calcium silicates
  • Olivine ((Mg,Fe)₂SiO₄) - Dominant in Earth's upper mantle
  • Clay minerals - Hydrated aluminum and magnesium silicates
Oxide Minerals
  • Hematite (Fe₂O₃) - Primary iron ore mineral
  • Magnetite (Fe₃O₄) - Magnetic iron oxide
  • Corundum (Al₂O₃) - Aluminum oxide (sapphire and ruby)
  • Rutile (TiO₂) - Titanium dioxide
  • Cuprite (Cu₂O) - Copper oxide ore
Carbonate Minerals
  • Calcite (CaCO₃) - Primary component of limestone and marble
  • Dolomite (CaMg(CO₃)₂) - Calcium magnesium carbonate
  • Siderite (FeCO₃) - Iron carbonate

Hydrospheric Distribution

Water (H₂O) contains 88.8% Oxygen by mass, making Earth's hydrosphere a massive Oxygen reservoir:

  • Oceans - 1.37 billion km³ containing ~1.2 × 10¹⁶ tons of Oxygen
  • Ice caps and glaciers - 24.4 million km³ of frozen water
  • Groundwater - 23.4 million km³ in aquifers worldwide
  • Lakes and rivers - 178,000 km³ of fresh surface water
  • Atmospheric water vapor - 12,900 km³ in constant circulation

Dissolved Oxygen in Natural Waters

Aquatic ecosystems depend on dissolved Oxygen (DO) levels:

  • Cold freshwater - Up to 14.6 mg/L at 0°C (ice-cold mountain streams)
  • Temperate lakes - 8-12 mg/L seasonal variation due to temperature
  • Tropical waters - 6-8 mg/L in warm surface waters
  • Seawater - 6-8 mg/L, varying with temperature and salinity
  • Deep ocean - 2-6 mg/L in Oxygen minimum zones

Biological Oxygen Production

Photosynthetic organisms are the ultimate source of Earth's Oxygen:

  • Marine phytoplankton - Produce 50-85% of Earth's Oxygen
  • Tropical rainforests - Amazon rainforest produces ~20% of atmospheric Oxygen
  • Boreal forests - Northern coniferous forests contribute significantly
  • Grasslands and crops - Agricultural areas and prairies
  • Cyanobacteria - Blue-green algae in both marine and freshwater environments

Extraterrestrial Oxygen

Oxygen occurs throughout the solar system and universe:

  • Mars atmosphere - 0.13% Oxygen, mostly from CO₂ photodissociation
  • Europa's atmosphere - Thin Oxygen atmosphere from water ice radiolysis
  • Comets - Water ice contains frozen Oxygen
  • Meteorites - Oxide minerals provide clues about early solar system
  • Exoplanet atmospheres - Oxygen signatures sought as potential biosignatures

Discovery

ARCHIVED
1774
Joseph Priestley and Carl Wilhelm Scheele

Safety Information

CRITICAL

Safety Information and Handling Pre
cautions

EXTREME FIRE HAZARD: Oxygen greatly accelerates combustion and can cause explosive fires with oils, greases, and organic materials.
Oxygen-enriched atmospheres make normally non-flammable materials burn violently.

Fire and Explosion Hazards

Oxygen's role in combustion creates severe safety risks:

High-Pressure Oxygen Hazards

DANGER: High-pressure Oxygen systems can cause explosive decompression, severe burns, and death.
Never use Oxygen with oil or grease-contaminated equipment.

Compressed Oxygen safety measures:

Medical Oxygen Safety

Healthcare Oxygen administration requires careful monitoring:

Occupational Exposure Limits

OSHA and regulatory standards for workplace Oxygen:

Cryogenic Oxygen Hazards

Liquid Oxygen (LOX) at -183°C presents additional dangers:

First Aid and Emergency Response

Emergency procedures for Oxygen incidents:

Environmental and Disposal Considerations

Environmental impact and waste management:

Transportation Safety

DOT regulations for Oxygen transport:

Knowledge Database

Essential information about Oxygen (O)

Oxygen is unique due to its atomic number of 8 and belongs to the Nonmetal category. With an atomic mass of 15.999000, it exhibits distinctive properties that make it valuable for various applications.

Its electron configuration ([He] 2s² 2p⁴) determines its chemical behavior and bonding patterns.

Oxygen has several important physical properties:

Density: 0.0014 g/cm³

Melting Point: 54.36 K (-219°C)

Boiling Point: 90.20 K (-183°C)

State at Room Temperature: Gas

Atomic Radius: 60 pm

Oxygen has various important applications in modern technology and industry:

Industrial Applications and Manufacturing

Steel and Metal Production

The largest industrial use of Oxygen is in steel manufacturing, where it dramatically improves efficiency and quality:

  • Basic Oxygen Furnace (BOF) - Pure Oxygen is blown through molten iron to remove carbon, producing high-quality steel in 30-40 minutes instead of hours
  • Electric Arc Furnace (EAF) - Oxygen injection increases melting rates and improves energy efficiency in recycling steel scrap
  • Cutting and welding - Oxy-acetylene and oxy-fuel torches reach temperatures over 3,500°C for precise metal cutting
  • Copper smelting - Oxygen enrichment reduces fuel consumption and increases production rates
  • Aluminum production - Oxygen helps remove impurities during aluminum refining processes

Chemical Manufacturing and Processing

Oxygen serves as a critical oxidizing agent in numerous industrial processes:

  • Ethylene oxide production - Direct oxidation of ethylene produces this key chemical intermediate for antifreeze and plastics
  • Vinyl chloride synthesis - Oxygen-based processes create the precursor for PVC plastic production
  • Propylene oxide manufacturing - Essential for producing polyurethane foams and propylene glycol
  • Titanium dioxide production - Oxygen helps create the white pigment used in paints, plastics, and paper
  • Hydrogen peroxide synthesis - Anthraquinone process uses Oxygen to produce this versatile oxidizing agent

Pulp and Paper Industry

Oxygen revolutionized paper manufacturing through environmentally friendly bleaching:

  • Oxygen delignification - Removes lignin from wood pulp without chlorine compounds
  • Ozone bleaching - Generates bright white paper with minimal environmental impact
  • Hydrogen peroxide bleaching - Oxygen-based bleaching creates high-quality recycled paper
  • Biological treatment - Oxygen enhances bacterial breakdown of organic pollutants in paper mill wastewater

Wastewater Treatment and Environmental Applications

Oxygen-based technologies clean water and reduce pollution:

  • Activated sludge process - Aerobic bacteria use Oxygen to break down organic pollutants
  • Ozonation - Ozone (O₃) destroys bacteria, viruses, and organic contaminants
  • Advanced oxidation processes - Hydroxyl radicals generated from Oxygen compounds eliminate persistent pollutants
  • Groundwater remediation - Oxygen injection stimulates biodegradation of soil contaminants
  • Aquaculture - Oxygen injection maintains fish health in intensive farming operations

Aerospace and Rocket Propulsion

Liquid Oxygen (LOX) is the most widely used rocket oxidizer:

  • Space Shuttle program - LOX and liquid hydrogen powered the main engines
  • SpaceX Falcon rockets - Use RP-1 fuel with liquid Oxygen oxidizer
  • Blue Origin - BE-4 engines burn methane with liquid Oxygen
  • Life support systems - Oxygen generation and recycling for spacecraft and space stations
  • Hypersonic flight - Scramjet engines use atmospheric Oxygen for high-speed propulsion

Glass Manufacturing

Oxygen combustion improves glass production efficiency and quality:

  • Oxy-fuel furnaces - Pure Oxygen combustion reaches higher temperatures with less fuel
  • Reduced emissions - Lower NOx production compared to air-fuel combustion
  • Improved glass quality - Higher temperatures enable better melting and homogenization
  • Energy efficiency - 15-50% reduction in fuel consumption compared to conventional furnaces
1774
Joseph Priestley and Carl Wilhelm Scheele

Discovered by: Joseph Priestley and Carl Wilhelm Scheele

Year of Discovery: 1774

Universal Abundance and Natural Sources

Cosmic and Stellar Origin

Oxygen is the third most abundant element in the universe, comprising approximately 1% of all atoms. It is primarily formed through stellar nucleosynthesis in massive stars:

  • Alpha process - Silicon burning in stars produces Oxygen through fusion reactions
  • Helium burning - Triple-alpha process in red giant stars creates carbon, which fuses with helium to form Oxygen
  • Supernova nucleosynthesis -
    Explosive stellar death disperses Oxygen throughout galaxies
  • Stellar winds - Evolved stars continuously enrich interstellar medium with Oxygen

The Oxygen in our solar system formed approximately 4.

6 billion years ago from the gravitational collapse of an Oxygen-rich molecular cloud.

Atmospheric Abundance

Earth's atmosphere contains 20.946% Oxygen by volume, representing the second most abundant atmospheric gas after nitrogen. This massive reservoir contains approximately 1.2 × 10¹⁵ tons of Oxygen gas.

Amazing Fact: Virtually all atmospheric Oxygen is biogenic - produced by photosynthetic organisms over billions of years. The Great Oxidation Event 2.4 billion years ago fundamentally changed Earth's atmosphere.

The atmospheric Oxygen cycle involves constant exchange between:

  • Photosynthesis - Plants, algae, and cyanobacteria produce ~330 billion tons of O₂ annually
  • Respiration - Living organisms consume Oxygen for cellular energy production
  • Combustion - Natural and human-caused fires consume atmospheric Oxygen
  • Chemical weathering - Rock oxidation slowly removes Oxygen from the atmosphere

Crustal and Lithospheric Abundance

Oxygen dominates Earth's crust, comprising approximately 46.1% by weight - making it the most abundant element in the solid Earth. Major Oxygen-bearing minerals include:

Silicate Minerals (95% of crust)
  • Quartz (SiO₂) - Pure silicon dioxide, abundant in sandstone and granite
  • Feldspar group - Potassium, sodium, and calcium aluminosilicates
  • Pyroxene and amphibole - Iron, magnesium, and calcium silicates
  • Olivine ((Mg,Fe)₂SiO₄) - Dominant in Earth's upper mantle
  • Clay minerals - Hydrated aluminum and magnesium silicates
Oxide Minerals
  • Hematite (Fe₂O₃) - Primary iron ore mineral
  • Magnetite (Fe₃O₄) - Magnetic iron oxide
  • Corundum (Al₂O₃) - Aluminum oxide (sapphire and ruby)
  • Rutile (TiO₂) - Titanium dioxide
  • Cuprite (Cu₂O) - Copper oxide ore
Carbonate Minerals
  • Calcite (CaCO₃) - Primary component of limestone and marble
  • Dolomite (CaMg(CO₃)₂) - Calcium magnesium carbonate
  • Siderite (FeCO₃) - Iron carbonate

Hydrospheric Distribution

Water (H₂O) contains 88.8% Oxygen by mass, making Earth's hydrosphere a massive Oxygen reservoir:

  • Oceans - 1.37 billion km³ containing ~1.2 × 10¹⁶ tons of Oxygen
  • Ice caps and glaciers - 24.4 million km³ of frozen water
  • Groundwater - 23.4 million km³ in aquifers worldwide
  • Lakes and rivers - 178,000 km³ of fresh surface water
  • Atmospheric water vapor - 12,900 km³ in constant circulation

Dissolved Oxygen in Natural Waters

Aquatic ecosystems depend on dissolved Oxygen (DO) levels:

  • Cold freshwater - Up to 14.6 mg/L at 0°C (ice-cold mountain streams)
  • Temperate lakes - 8-12 mg/L seasonal variation due to temperature
  • Tropical waters - 6-8 mg/L in warm surface waters
  • Seawater - 6-8 mg/L, varying with temperature and salinity
  • Deep ocean - 2-6 mg/L in Oxygen minimum zones

Biological Oxygen Production

Photosynthetic organisms are the ultimate source of Earth's Oxygen:

  • Marine phytoplankton - Produce 50-85% of Earth's Oxygen
  • Tropical rainforests - Amazon rainforest produces ~20% of atmospheric Oxygen
  • Boreal forests - Northern coniferous forests contribute significantly
  • Grasslands and crops - Agricultural areas and prairies
  • Cyanobacteria - Blue-green algae in both marine and freshwater environments

Extraterrestrial Oxygen

Oxygen occurs throughout the solar system and universe:

  • Mars atmosphere - 0.13% Oxygen, mostly from CO₂ photodissociation
  • Europa's atmosphere - Thin Oxygen atmosphere from water ice radiolysis
  • Comets - Water ice contains frozen Oxygen
  • Meteorites - Oxide minerals provide clues about early solar system
  • Exoplanet atmospheres - Oxygen signatures sought as potential biosignatures

Earth's Abundance: 4.61e-1

Universe Abundance: 1.04e-2

General Safety: Oxygen should be handled with standard laboratory safety precautions including protective equipment and proper ventilation.

Safety Information and Handling Pre
cautions

EXTREME FIRE HAZARD: Oxygen greatly accelerates combustion and can cause explosive fires with oils, greases, and organic materials.
Oxygen-enriched atmospheres make normally non-flammable materials burn violently.

Fire and Explosion Hazards

Oxygen's role in combustion creates severe safety risks:

  • Combustion acceleration - Materials burn 3-5 times faster in pure Oxygen
  • Lowered ignition temperatures - Many materials ignite at much lower temperatures
  • Explosive potential - Oil and grease can explode on contact with high-pressure Oxygen
  • Clothing fires - Synthetic fabrics become extremely flammable in Oxygen-rich environments
  • Hot surfaces - Cigarettes, sparks, and hot metal can trigger violent combustion

High-Pressure Oxygen Hazards

DANGER: High-pressure Oxygen systems can cause explosive decompression, severe burns, and death.
Never use Oxygen with oil or grease-contaminated equipment.

Compressed Oxygen safety measures:

Medical Oxygen Safety

Healthcare Oxygen administration requires careful monitoring:

Occupational Exposure Limits

OSHA and regulatory standards for workplace Oxygen:

5% to 23.5% in workplace atmospheres
  • Oxygen deficiency - Below 19.5% requires supplied air or evacuation
  • Oxygen enrichment - Above 23.5% creates fire and explosion hazards
  • Confined spaces - Continuous monitoring required in tanks, vessels, and enclosed areas
  • Hot work permits - Special pre
    cautions for welding and cutting in Oxygen-enriched areas
  • Cryogenic Oxygen Hazards

    Liquid Oxygen (LOX) at -183°C presents additional dangers:

    First Aid and Emergency Response

    Emergency procedures for Oxygen incidents:

    Environmental and Disposal Considerations

    Environmental impact and waste management:

    Transportation Safety

    DOT regulations for Oxygen transport:

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