Q104 / 180 · NEET 2026 (Cancelled) · Chemistry

Given below are certain reactions. Identify the reaction for which $K_p \neq K_c$ :

  • A
    $\text{H}_2\text{O (g)} + \text{CO (g)} \rightleftharpoons \text{H}_2\text{(g)} + \text{CO}_2\text{(g)}$
  • Correct answer
    B
    $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$
  • C
    $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI (g)}$
  • D
    $\text{N}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{NO (g)}$

Solution

The relation between $K_p$ and $K_c$ is given by $K_p = K_c(RT)^{\Delta n_g}$, where $\Delta n_g$ is the difference between the number of moles of gaseous products and gaseous reactants.

For $K_p \neq K_c$, $\Delta n_g$ must be non-zero.

For $\text{H}_2\text{O (g)} + \text{CO (g)} \rightleftharpoons \text{H}_2\text{(g)} + \text{CO}_2\text{(g)}$, $\Delta n_g = 2 - 2 = 0 \Rightarrow K_p = K_c$

For $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$, $\Delta n_g = 2 - 4 = -2 \Rightarrow K_p \neq K_c$

For $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI (g)}$, $\Delta n_g = 2 - 2 = 0 \Rightarrow K_p = K_c$

For $\text{N}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{NO (g)}$, $\Delta n_g = 2 - 2 = 0 \Rightarrow K_p = K_c$

Answer: $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$

Hence, the correct answer is option: 'B'.

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