CBSE Class 12 · 2023 · Modern PhysicsLong Answer

The stopping potential (where each curve meets the potential axis on the retarding side) fixes the maximum kinetic energy, through $e{V}_0=h\nu -{\varphi }_0$.
(i) **Highest frequency $\to$ beam B**: it has the greatest stopping potential, hence the largest $K_{max}$ and (for the same metal) the highest frequency.
(ii) **Longest wavelength $\to$ beam C**: it has the smallest stopping potential, hence the lowest frequency and therefore the longest wavelength ($\lambda =c/\nu$).
(iii) **Maximum momentum $\to$ beam B**: the largest $K_{max}$ means the largest electron speed, and momentum $p=mv=\sqrt{2m{K}_{max}}$ is greatest for beam B.