JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Chemical Kinetics

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Observe the following reactions at T(K).
I. A → products.
II. 5Br⁻(aq) + BrO₃⁻(aq) + 6H⁺(aq) → 3Br₂(aq) + 3H₂O(l)
Both the reactions are started at 10:00 am. The rates of these reactions at 10:10 am are the same. The value of −Δ[Br⁻]/Δt at 10:10 am is 2 × 10⁻⁴ mol L⁻¹ min⁻¹. The concentration of A at 10:10 am is 10⁻² mol L⁻¹. What is the first order rate constant (in min⁻¹) of reaction I?

(A) $2 \times 1 0^{- 3}$
(B) $1 0^{- 3}$
(C) $1 0^{- 2}$
(D) $4 \times 1 0^{- 3}$ ✓ Correct

Answer: (D)

Solution

For the bromate--bromide reaction the rate is

- \frac{1}{5} \frac{Δ [ B r ^{-} ]}{Δ t} = \frac{1}{5} (2 \times 1 0^{- 4}) = 4 \times 1 0^{- 5} mol L^{- 1} mi n^{- 1}

. Since the two reactions proceed at equal rates at that instant, reaction I also has this rate. For the first-order reaction I,

k = \frac{rate}{[ A ]} = \frac{4 \times 1 0 ^{- 5}}{1 0 ^{- 2}} = 4 \times 1 0^{- 3} mi n^{- 1}

JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Single correct option

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JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Chemical Kinetics

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