Einstein's Photoelectric Equation is :

K_max = hv - Φ

where v is the frequency of the incident radiation and K_max is the maximum possible kinetic energy of photoelectron. The work function Φ is given as :

Φ = hv₀ . In terms of stopping potential, K_max = eV_0.

What is the charge on a photon?

same as neutron

The correct answer is Option 3 : same as neutron

A photon has no electric charge, just like a neutron. Therefore, the charge on a photon is zero (neutral).