The reaction in which dihydrogen is acting as an oxidising agent is

• A

  $\begin{aligned} & \mathrm{Pd}^{2+}{ }_{(a q)}+\mathrm{H}_{2(g)} \longrightarrow \mathrm{Pd}_{(s)}+2 \mathrm{H}_{(a q)}^{+}\end{aligned}$
• B

  $\mathrm{CuO}_{(s)}+\mathrm{H}_{2(g)} \longrightarrow \mathrm{Cu}_{(s)}+\mathrm{H}_2 \mathrm{O}_{(g)}$
• Correct answer
  C

  $2 \mathrm{Na}_{(s)}+\mathrm{H}_{2(g)} \longrightarrow 2 \mathrm{NaH}_{(s)}$
• D

  $\begin{aligned} & \mathrm{O}_{2_{(g)}}+2 \mathrm{H}_{2(g)} \longrightarrow 2 \mathrm{H}_2 \mathrm{O}_{(l)}\end{aligned}$

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