The standard reduction potentials at $295 \mathrm{K}$ for the following half cells are given below:

${{\mathrm{NO}}_3}^{-}+4{\mathrm{H}}^{+}+3{\mathrm{e}}^{-}\to \mathrm{NO}\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}$	${\mathrm{E}}^{\mathrm{o}}=0.97 \mathrm{V}$
${\mathrm{V}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to \mathrm{V}\left(\mathrm{s}\right)$	${\mathrm{E}}^{\mathrm{o}}=-1.19 \mathrm{V}$
${\mathrm{Fe}}^{3+}\left(\mathrm{aq}\right)+3{\mathrm{e}}^{-}\to \mathrm{Fe}\left(\mathrm{s}\right)$	${\mathrm{E}}^{\mathrm{o}}=-0.04 \mathrm{V}$
${\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)+{\mathrm{e}}^{-}\to \mathrm{Ag}\left(\mathrm{s}\right)$	${\mathrm{E}}^{\mathrm{o}}=0.80 \mathrm{V}$
${\mathrm{Au}}^{3+}\left(\mathrm{aq}\right)+3{\mathrm{e}}^{-}\to \mathrm{Au}\left(\mathrm{s}\right)$	${\mathrm{E}}^{\mathrm{o}}=1.40 \mathrm{V}$

The number of metal(s) which will be oxidised by ${{\mathrm{NO}}_3}^{-}$ in aqueous solution is _____.

For feasibility, check , ${{\mathrm{E}}^{\mathrm{o}}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cathode}\left(\mathrm{reduction}\right)}^{\mathrm{o}}-{\mathrm{E}}_{\mathrm{anode}\left(\mathrm{oxidation}\right)}^{\mathrm{o}}>0$

The ${\mathrm{E}}^{\mathrm{o}}$ values when metal acts as anode and ${\mathrm{NO}}_3^{-}$ reaction is cathodic reaction.

For Vanadium metal, ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}=0.97+1.19=2.16\mathrm{V}$

For Iron metal, ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}=0.97+0.04=1.01\mathrm{V}$

For silver metal, ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}=0.97-0.80=0.17\mathrm{V}$

For Gold metal, ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}=0.97-1.140=-0.17\mathrm{V}$

For electrodes having oxidation potential greater than $-0.97 \mathrm{V}$, ${{\mathrm{E}}^{\mathrm{o}}}_{\mathrm{cell}}>0$

$\therefore \mathrm{Ag}, \mathrm{Fe}$ and $\mathrm{V}$ can be oxidised