If ϕ_o is the work function of a metal surface and ν is the frequency of the incident light, then the maximum kinetic energy of the emitted electron is equal to:

CONCEPT:

Photoelectric Effect:

• When the light of a sufficiently small wavelength is incident on the metal surface, electrons are ejected from the metal instantly. This phenomenon is called the photoelectric effect.​
• Einstein’s equation of photoelectric effect:

⇒ KEmax = hν - ϕo

Where h = Planck's constant, ν = frequency of incident radiation, ϕo = work function, and KE_max = maximum kinetic energy of electrons.

​Laws of Photoelectric Effect:

1. For a light of any given frequency; (f > fTh) photoelectric current is directly proportional to the intensity of light
2. For any given material, there is a certain minimum frequency, called threshold frequency, below which the emission of photoelectrons stops completely, no matter how high is the intensity of incident light.
3. The maximum kinetic energy of the photoelectrons is found to increase with the increase in the frequency of incident light, provided the frequency (f > fTh) exceeds the threshold limit. The maximum kinetic energy is independent of the intensity of light.
4. The photoelectric emission is an instantaneous process without any apparent time lag (10-9 sec or less), even when the intensity of the incident radiation is made extremely low.​

• Hence, option 2 is correct.