Photoelectric effect, phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it. In a broader definition, the radiant energy may be infrared, visible, or ultraviolet light, X-rays, or gamma rays; the material may be a solid, liquid, or gas; and the released particles may be ions (electrically charged atoms or molecules) as well as electrons.

In a photon-electron collision both total energy and total momentum are conserved. As in the case of the Compton effect,  when a photon with some energy collides with a stationary electron, some of the energy and momentum is transferred to the electron  but both energy and momentum are conserved in this elastic collision.so the correct option would be option B.

Cathode rays are high energetic electron beam.
Specific charge of cathode rays = e ​/m_{e ​}
Specific charge of positive rays =∣e ∣/m ​
Since the mass of positive rays is much larger than that of cathode rays, so the specific charge for positive rays is much smaller than that for cathode rays.

Photoelectrons will come out from the surface of the metal only if it gets enough energy during the irradiation the energy needed depends on the metal and the max energy that can be provided on the light.

Davisson and Germer Experiment, for the first time, proved the wave nature of electrons and verified the de Broglie equation. de Broglie argued the dual nature of matter back in 1924, but it was only later that Davisson and Germer experiment verified the results. The results established the first experimental proof of quantum mechanics. In this experiment, we will study the scattering of electrons by a Ni crystal.

Voltage across the electrodes of a cathode ray gun, V=500V
Charge of the electron=1.6x10^-19
Energy=eV
E= 1.6x10^-19 x 500
E=800 x 10^-19 J
E=8 x 10^-17 J

Incident frequency=work function + kinetic energy.
incident frequency=E.
therefore, hc/λ=E
for energy in e.v &wavelength in Angstrom...
Now,
we know,
E=12400/λÅ
E(in e.v)=12400/1000.=12.4e.v

Given, the maximum kinetic energy: K_max ​=4eV
If V0 ​be the stopping potential, then K_max ​=eV₀ ​
⇒eV_{0 ​} =4eV  
⇒V₀ ​=4V

Photoelectric cell or photocell, device whose electrical characteristics (e.g., current, voltage, or resistance) vary when light is incident upon it. The most common type consists of two electrodes separated by a light-sensitive semiconductor material.
The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner can be called photoelectrons.

A particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass.