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Science (086) — CBSE Class 10 board question

Q1. [1] § 5.2.1 Autotrophic Nutrition
The following events occur during the process of photosynthesis. Choose the option that indicates the correct events. (i) Oxidation of carbon dioxide to carbohydrates (ii) Conversion of light energy into chemical energy (iii) Absorption of light energy by chlorophyll (iv) Conversion of hydrogen and oxygen into water
  1. (A) (i) and (ii)
  2. (B) (ii) and (iii)
  3. (C) (iii) and (iv)
  4. (D) (i) and (iv)
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Model Answer

(B) (ii) and (iii)

The correct events are: (iii) Absorption of light energy by chlorophyll, and (ii) Conversion of light energy to chemical energy (along with splitting of water into hydrogen and oxygen). Carbon dioxide is reduced (not oxidised) to carbohydrates, and water is produced by splitting, not formed from hydrogen and oxygen.

Source: Life Processes, Section 5.2.1

Explanation

The textbook explicitly lists the three events of photosynthesis: absorption of light by chlorophyll, conversion of light energy to chemical energy + splitting of water, and reduction of CO₂ to carbohydrates. Statement (i) is wrong because CO₂ is reduced, not oxidised. Statement (iv) is wrong because water is split into hydrogen and oxygen, not formed from them. Examiners expect students to know these distinctions precisely.

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