Quantrex Academy · Free JEE Main PYQ solutions
JEE Main Chemistry Chemical Kinetics 2026 JEE Main 2026 (23 January Shift 2)

JEE Main Chemistry Question (2026) — Solution

Question

Observe the following reactions at T ( K ). I. A products. II. 5 Br ^ - ( aq )+ BrO _ 3 ^ - ( aq )+6 H ^ + ( aq ) 3 Br _ 2 ( aq )+3 H _ 2 O ( l ) Both the reactions are started at 10.00 am. The rates of these reactions at 10.10 am are same. The value of - [ Br ^ - ] t 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 ?

Options

  1. A. 10^ -2
  2. B. 10^ -3
  3. C. 2 10^ -3
  4. D. 4 10^ -3

Answer

D. 4 10^ -3

Step-by-step solution

For reaction II: 5Br^- + BrO_3^- + 6H^+ 3Br_2 + 3H_2O, The overall reaction rate is: r = - 1 5 [Br^-] t = - 1 3 [Br_2] t . Given [Br^-] t = 2 10^ -4 mol L^ -1 min^ -1 The reaction rate is r = 2 10^ -4 5 = 4 10^ -5 mol L^ -1 min^ -1 . Since the rates of both reactions are equal at 10.10 am and reaction I is first-order: r = k[A], so 4 10^ -5 = k 10^ -2 , giving k = 4 10^ -3 min^ -1 .

Practice more on Quantrex App →

Related: Chemistry — Chemical Kinetics · All PYQ Banks