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Assertion (A): The… (Class 12 Biology SQP 2026-27, Q15)

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BiologyCBSE Class 12 · Sample paper, session 2026-27 · 1 mark · Assertion-reason

CBSE Class 12 Biology sample paper 2026-27: question 15

From the official CBSE sample question paper for 2026-27, section A, question 15, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q15 · 1 mark · Assertion-reasonCompetency-basedMicrobes in Human Welfare

Assertion (A): The primary goal of sewage treatment is to eliminate all organic matter from the effluent.
Reason (R): High BOD indicates a low level of organic matter in the water, which can lead to increased oxygen consumption by microorganisms, potentially harming aquatic life.

  1. (A)Both A and R are true and R is the correct explanation of A.
  2. (B)Both A and R are true but R is not the correct explanation of A.
  3. (C)A is true but R is false.
  4. (D)A is False but R is true.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

Open one hint at a time and try again before the next.

Hint 1

What does BOD measure?

Hint 2

More organic matter means more oxygen is consumed by microbes.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Sewage treatment aims to remove organic matter and lower the BOD of the effluent.

  2. R is false, because a high BOD indicates a high level of organic matter, not a low one. Option (C).

    1 mark

Answer: (C)

Where the marks are

  • Identifies that R wrongly links high BOD with low organic matter (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Microbes in Human Welfare, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.