Chemistry Q60 – NEET-UG 2026

Home Chemistry Chemical KineticsQuestion #288

2 A \overset{k}{\to} B

is a zero-order reaction, where

k = 1.0 {mol L}^{- 1} {min}^{- 1}

. If the initial concentration of A is

2 M

, then the time taken to complete

75 %

of the reaction will be

Clue 1 of 3: Reaction Order

Understand the integrated rate law for a zero-order reaction.

🧠 Full Solution Path

Step 1: Identify the Reaction Order and Rate Law✦ Active

The problem states that the reaction is a zero-order reaction. The integrated rate law for a zero-order reaction is given by the equation:

[A]_{t} = [A]_{0} - k t

This can be rearranged to solve for time $t$ :

t = \frac{[A]_{0} - [A]_{t}}{k}

Step 2: Calculate the Concentration of Reactant Remaining○ Expand

The initial concentration of A is given as $[A]_{0} = 2 M$ . The reaction is $75 %$ complete, which means $75 %$ of the initial reactant has been consumed. Therefore, $25 %$ of the reactant remains.

[A]_{t} = (1 - 0.75) \times [A]_{0} = 0.25 \times 2 M = 0.5 M

💡 Teacher's Secret Hint

Ensure to calculate the remaining concentration, not the consumed amount, for the $[A]_{t}$ term in the rate law.

Step 3: Calculate the Time Taken○ Expand

Substitute the initial concentration, remaining concentration, and the rate constant into the rearranged integrated rate law:

t = \frac{[A]_{0} - [A]_{t}}{k} = \frac{2 M - 0.5 M}{1.0 {mol L}^{- 1} {min}^{- 1}}

Since $1 M = 1 {mol L}^{- 1}$ :

t = \frac{1.5 M}{1.0 {M min}^{- 1}} = 1.5 min

💡 Teacher's Secret Hint

Always check that the units cancel out correctly to give the desired unit for time.

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Chemistry Question 60 – NEET-UG 2026

Clue 1 of 3: Reaction Order

🧠 Full Solution Path