Oxygen – Complete Guide for Students & Chemistry Enthusiasts
1. Basic Information
- Symbol: O
- Atomic Number: 8
- Atomic Mass: 15.999 u
- Electronic Configuration: 1s² 2s² 2p⁴
- Group / Period: Group 16 (Chalcogens), Period 2
- State at Room Temperature: Gas (diatomic molecule O₂)
- Density: 1.429 g/L at 0°C
- Melting Point: 54.36 K (-218.79°C)
- Boiling Point: 90.20 K (-182.95°C)
- Oxidation States: -2 (most common), -1 (in peroxides), +2, +1 (rare)
2. Occurrence
- Earth’s Crust: ~46.6% by weight (mainly in oxides and silicates)
- Atmosphere: ~21% by volume as O₂
- In Water: H₂O contains 2/3 of its weight from oxygen
- In Living Organisms: Found in carbohydrates, proteins, fats, and nucleic acids
3. Allotropes of Oxygen
- Dioxygen (O₂): Normal oxygen gas, supports life, pale blue liquid at low temperatures.
- Ozone (O₃): Triatomic form, strong oxidizer, absorbs UV radiation in the stratosphere.
4. Physical Properties
- Colorless, odorless, and tasteless gas at room temperature
- Slightly soluble in water
- Supports combustion but is not flammable itself
- Paramagnetic (has unpaired electrons)
5. Chemical Properties
- Combustion: Supports burning of fuels. Example: C + O₂ → CO₂
- Formation of Oxides: Reacts with metals and non-metals. Example: 2Mg + O₂ → 2MgO
- Oxidizing Agent: Strong oxidizer in many reactions. Example: 2H₂O₂ → 2H₂O + O₂
6. Industrial Production
- Fractional Distillation of Liquid Air: Main commercial method
- Electrolysis of Water: Produces oxygen and hydrogen
- Chemical Methods: Decomposition of potassium chlorate (KClO₃) using MnO₂ as a catalyst
7. Uses of Oxygen
- Medical: Oxygen therapy for patients with respiratory problems
- Industrial: Steel production, welding, and cutting metals
- Chemical Industry: Manufacture of acids, oxidizing agents, and ozone
- Aerospace: Fuel for rockets in liquid oxygen (LOX) form
- Environmental: Treatment of sewage, water purification
8. Biological Importance
- Required for respiration in humans, animals, and plants
- Essential in cellular energy production (ATP) in mitochondria
- Present in water and most biomolecules
9. Safety and Precautions
- Oxygen itself is non-flammable but accelerates fire
- Avoid storing near flammable materials
- Handle liquid oxygen carefully; it can cause frostbite
10. Fun Facts
- O₂ is responsible for the blue color of the sky in small quantities
- Ozone layer protects Earth from harmful UV rays
- Oxygen was discovered independently by Carl Wilhelm Scheele (1772) and Joseph Priestley (1774)
Oxygen Element – Important MCQs
Q1: What is the atomic number of Oxygen?
- A) 6
- B) 7
- C) 8
- D) 9
Answer: C) 8
Explanation: Oxygen has 8 protons in its nucleus, hence its atomic number is 8.
Explanation: Oxygen has 8 protons in its nucleus, hence its atomic number is 8.
Q2: What is the common allotrope of Oxygen found in the atmosphere?
- A) O₃ (Ozone)
- B) O₂ (Dioxygen)
- C) O₄
- D) O₅
Answer: B) O₂
Explanation: Dioxygen (O₂) is the most stable and common form of oxygen in the air.
Explanation: Dioxygen (O₂) is the most stable and common form of oxygen in the air.
Q3: Oxygen belongs to which group in the periodic table?
- A) Group 16
- B) Group 15
- C) Group 17
- D) Group 18
Answer: A) Group 16
Explanation: Oxygen is a chalcogen and belongs to group 16 (VIA) of the periodic table.
Explanation: Oxygen is a chalcogen and belongs to group 16 (VIA) of the periodic table.
Q4: What is the electron configuration of Oxygen?
- A) 1s² 2s² 2p⁴
- B) 1s² 2s² 2p³
- C) 1s² 2s² 2p⁶
- D) 1s² 2s¹ 2p⁵
Answer: A) 1s² 2s² 2p⁴
Explanation: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p orbitals.
Explanation: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p orbitals.
Q5: Which of the following is an allotrope of oxygen used in the ozone layer?
- A) O₁
- B) O₂
- C) O₃
- D) O₄
Answer: C) O₃
Explanation: Ozone (O₃) protects Earth from harmful UV radiation.
Explanation: Ozone (O₃) protects Earth from harmful UV radiation.
Q6: What is the most common oxidation state of Oxygen?
- A) -2
- B) -1
- C) +1
- D) 0
Answer: A) -2
Explanation: Oxygen usually forms O²⁻ ions in compounds, giving it an oxidation state of -2.
Explanation: Oxygen usually forms O²⁻ ions in compounds, giving it an oxidation state of -2.
Q7: At what temperature does Oxygen boil?
- A) 90 K
- B) 77 K
- C) 85 K
- D) 100 K
Answer: C) 90 K
Explanation: Oxygen boils at 90.2 K (-182.95°C) under standard pressure.
Explanation: Oxygen boils at 90.2 K (-182.95°C) under standard pressure.
Q8: Oxygen is essential for which biological process?
- A) Photosynthesis
- B) Respiration
- C) Fermentation
- D) Nitrogen fixation
Answer: B) Respiration
Explanation: Oxygen is required for cellular respiration to release energy from glucose.
Explanation: Oxygen is required for cellular respiration to release energy from glucose.
Q9: Which compound contains the highest percentage of oxygen by mass?
- A) H₂O
- B) CO₂
- C) O₃
- D) Na₂O
Answer: C) O₃
Explanation: Ozone is pure oxygen (O₃), so it has 100% oxygen by mass.
Explanation: Ozone is pure oxygen (O₃), so it has 100% oxygen by mass.
Q10: Oxygen was discovered by which scientist?
- A) Antoine Lavoisier
- B) Joseph Priestley
- C) Carl Wilhelm Scheele
- D) All of the above
Answer: D) All of the above
Explanation: Scheele, Priestley, and Lavoisier independently contributed to the discovery and identification of oxygen.
Explanation: Scheele, Priestley, and Lavoisier independently contributed to the discovery and identification of oxygen.
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