Which of the following gases is absorbed from the air due to photosynthesis?

Step 1: Analyze the question The question asks which gas plants take in from the air during photosynthesis.

Step 2: Explain the concept Photosynthesis is the process by which green plants make food (glucose) using sunlight and chlorophyll. The raw materials are carbon dioxide and water. The products are glucose and oxygen.

Word equation: Carbon (IV) oxide + water → (sunlight, chlorophyll) → glucose + oxygen

Balanced equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Step 3: Go through the options

• A. Carbon (II) oxide (CO): This is a poisonous gas from incomplete combustion. Plants do not use it for photosynthesis.
• B. Carbon (IV) oxide (CO₂): Plants absorb this through their stomata and use it to make glucose. ✔
• C. Nitrogen: This is the most abundant gas in air, but plants cannot absorb it directly. Bacteria must first fix it into nitrates or similar compounds.
• D. Noble gases: These are inert and not involved in photosynthesis.
• E. Oxygen: This is released during photosynthesis, not absorbed. Plants take in oxygen only for respiration.

Step 4: Answer The correct answer is B. Carbon (IV) oxide.

Tip: Remember "plants eat CO₂ and breathe out O₂" during photosynthesis. In exams, watch for options that name the product (oxygen) instead of the reactant (carbon (IV) oxide). Also remember that carbon (IV) oxide is the same as carbon dioxide (the Roman numeral shows the oxidation state of carbon).