More practice questions

4. Q4. In Ingenhousz’s experiment with an aquatic plant, where did bubbles form, and under what condition?

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   Around the green parts, in bright sunlight only; in the dark no bubbles formed. He later identified them as oxygen (NCERT page 134).

5. Q5. What is the “oxidation” product when purple and green sulphur bacteria use H_₂S as the hydrogen donor?

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   Sulphur or sulphate, depending on the organism, and not O_₂ (NCERT page 135).

6. Q6. In the water-oxidation half-reaction of photosynthesis, how many H_₂O must be oxidised to release six O_₂?

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   Twelve H_₂O: 12H_₂O → 6O_₂ + 24H^⁺ + 24e^⁻. The net overall equation cancels six waters after combining oxidation and reduction; isotope evidence establishes water as the source of evolved O_₂.