Which of the following reactions is an example of nucleophilic substitution reaction?

• Correct answer
  A

  $\mathrm{RX}+\mathrm{KOH} \longrightarrow \mathrm{ROH}+\mathrm{KX}$
• B

  $2 \mathrm{RX}+2 \mathrm{Na} \longrightarrow \mathrm{R}-\mathrm{R}+2 \mathrm{NaX}$
• C

  $\mathrm{RX}+\mathrm{H}_2 \longrightarrow \mathrm{RH}+\mathrm{HX}$
• D

  $\mathrm{RX}+\mathrm{Mg} \longrightarrow \mathrm{RMgX}$

Solution

Key Idea Nucleophilic substitution reactions involve substitution (replacement) of a group or atom by a nucleophile. $$ \begin{aligned} & \mathrm{KOH} \longrightarrow \mathrm{K}^{+}+\mathrm{OH}^{-} \\ & \mathrm{RX}+\underset{\text { nucleophile }}{\mathrm{OH}^{-}} \longrightarrow \mathrm{R}-\mathrm{OH}+\mathrm{KX} \\ & \end{aligned} $$

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