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Which of the following curve… (Class 12 Chemistry 2026, Q1)

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ChemistryCBSE Class 12 · Board exam 2026, set 56/1/1 · 1 mark · MCQ

CBSE Class 12 Chemistry 2026: question 1

Set in the CBSE Class 12 board exam of 2026, paper 56/1/1, section A, question 1, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q1 · 1 mark · MCQChemical Kinetics

Which of the following curve represents the first order reaction ?

  1. (A)Graph of t_{1/2} vs [R]_0: straight line rising from the origin
  2. (B)Graph of t_{1/2} vs [R]_0: horizontal line (constant)
  3. (C)Graph of Rate vs Concentration: horizontal line (constant)
  4. (D)Graph of Rate vs Concentration: decreasing curve

Figure in the paper: Four graphs. (A) t1/2 on y-axis vs [R]0 on x-axis: straight line through origin with positive slope. (B) t1/2 vs [R]0: horizontal line. (C) Rate vs Concentration: horizontal line. (D) Rate vs Concentration: curve decreasing steeply and flattening out. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 56/1/1.

Hints

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

Hint 1

Write the half-life expression for a first order reaction.

Hint 2

Check whether contains .

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. For a first order reaction, , which does not depend on .

  2. So the plot of against is a horizontal line. Graph (A) is for zero order, and graph (C) (rate constant with concentration) is also zero order. Correct option: (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Picks the constant vs graph, option (B) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Chemical Kinetics, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 56/1/1: 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.