For the equilibrium A ⇌ B , the variation of the rate of the forward (a) and reverse (b) reaction with time is given by :

Chemical Equilibrium PYQ — JEE Main 2020 · 4 Sep · Shift 1 · Q19 with Solution

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Correct answer: C

Understand the equilibrium process

For the reversible reaction $A \rightleftharpoons B$
- Initially, if we start with only $A$ $A$ , then:
  - Forward reaction rate is maximum at $t=0$ because concentration of $A$ is maximum.
  - Reverse reaction rate is zero at $t=0$ because initially $B$ is absent.
How rates change with time
- As time passes, $A$ is converted into $B$ .
- Therefore:
  - $[A]$ decreases, so the forward rate decreases with time.
  - $[B]$ increases, so the reverse rate increases with time.
At equilibrium

At equilibrium, $\text{rate of forward reaction} = \text{rate of reverse reaction}$

So the correct graph must show:
- Curve (a): starts high and decreases with time.
- Curve (b): starts from zero (or low value) and increases with time.
- Both curves eventually become equal and remain constant at equilibrium.
Match with options

The option representing this behavior is Option C.
Comparison with stored answer

Stored correct answer = C.

Our derived answer = C.

Hence, they agree.