If more than one species is available near the cathode,which species will undergo a reduction reaction? Provide suitable examples.

(N/A) When multiple species are available for reduction at the cathode,the species with the higher (more positive) standard electrode potential $(E^\circ)$ will be reduced preferentially.
This is because a higher $E^\circ$ value indicates a greater tendency to gain electrons.
Example: In an aqueous solution of $NaCl$,both $Na^+$ ions and $H_2O$ molecules are present near the cathode.
The reduction potentials are:
$Na^+ + e^- \rightarrow Na$ $(E^\circ = -2.71 \ V)$
$2H_2O + 2e^- \rightarrow H_2(g) + 2OH^-(aq)$ $(E^\circ = -0.83 \ V)$
Since $-0.83 \ V > -2.71 \ V$,water molecules are reduced at the cathode instead of $Na^+$ ions,resulting in the evolution of $H_2$ gas.