The difference between threshold wavelengths for two metal surfaces \( A \) and \( B \) having work function \( \phi_A = 9 \, \text{eV} \) and \( \phi_B = 4.5 \, \text{eV} \) in \( \text{nm} \) is: {Given, \( hc = 1242 \, \text{eV} \, \text{nm} \)}
\( 540 \)
\( 138 \)
\( 276 \)
\( 264 \)
