Einstein photo-electric equation states that $E_k = hv - Ø$. In the equation, $E_k$ refers to

Maximum kinetic energy of the emitted electrons

The correct answer is Option (4) → Maximum kinetic energy of the emitted electrons

$K.E._{max}=hv-\phi$

This is the photoelectric equation.

$K.E._{max}$ = Maximum kinetic energy of photoelectron

$hv$ = Energy of photon

$\phi$ = Work function