JEE Main 2026 — Chemistry Physical Chemistry

2026mcqmedium

$\mathrm{A} \rightarrow$ product (First order reaction). Three sets of experiment were performed for a reaction under similar experimental conditions:

Run $1 \Rightarrow 100 \mathrm{~mL}$ of 10 M solution of reactant A

Run $2 \Rightarrow 200 \mathrm{~mL}$ of 10 M solution of reactant A

Run $3 \Rightarrow 100 \mathrm{~mL}$ of 10 M solution of reactant $\mathrm{A}+100 \mathrm{~mL}$ of $\mathrm{H}_{2} \mathrm{O}$ added.

The correct variation of rate of reaction is

Official previous-year question

Held on 22 Jan 2026 · Verified 6 Jul 2026.

Options

A
Run $1<$ Run $2<$ Run 3
B
Run $3<$ Run $1<$ Run 2
C
Run $3<$ Run 1 = Run 2
D
Run $1=$ Run $2=$ Run 3

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Solution

For a first-order reaction, rate = $k[A]$ , where rate is directly proportional to reactant concentration.

Run 1: 100 mL of 10 M solution

Concentration = 10 M

Rate: $r_1 = k \times 10$

Run 2: 200 mL of 10 M solution

Concentration remains 10 M (increasing volume doesn't change concentration)

Rate: $r_2 = k \times 10$

Therefore $r_1 = r_2$

Run 3: 100 mL of 10 M solution + 100 mL of H₂O

Total moles of A = 10 M × 0.1 L = 1 mol

Total volume = 0.2 L

New concentration = 1 mol / 0.2 L = 5 M

Rate: $r_3 = k \times 5$

Therefore $r_3 < r_1 = r_2$

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Solution

For a first-order reaction, rate = $k[A]$ , where rate is directly proportional to reactant concentration.

Run 1: 100 mL of 10 M solution

Concentration = 10 M

Rate: $r_1 = k \times 10$

Run 2: 200 mL of 10 M solution

Concentration remains 10 M (increasing volume doesn't change concentration)

Rate: $r_2 = k \times 10$

Therefore $r_1 = r_2$

Run 3: 100 mL of 10 M solution + 100 mL of H₂O

Total moles of A = 10 M × 0.1 L = 1 mol

Total volume = 0.2 L

New concentration = 1 mol / 0.2 L = 5 M

Rate: $r_3 = k \times 5$

Therefore $r_3 < r_1 = r_2$

JEE Main 2026 — Chemistry Physical Chemistry

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Solution

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JEE Main Physical Chemistry in other years

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Organic Chemistry

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JEE Main 2026 — Chemistry Physical Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry