Correct option is : (3) 2 V
\( \mathrm{E}=\frac{\mathrm{h}_{\mathrm{c}}}{\lambda}=\frac{1240}{300} \mathrm{eV} \Rightarrow \mathrm{E}=4.1 \mathrm{eV}\)
\(\phi=2.13 \mathrm{evE}\)
\(\mathrm{E}=\phi+\mathrm{e} \Delta \mathrm{v}\)
\( 4.1 \mathrm{ev}=(2.13) \mathrm{ev}+\mathrm{e}(\Delta \mathrm{V}) \)
\(\Delta \mathrm{V}=4.1-2.13 \)
\(\Delta \mathrm{v}=1.97 \mathrm{~V} \approx 2 \mathrm{v}\)