The work function of aluminium is $4.2 \ eV$. If two photons, each of energy $3.5 \ eV$, strike an electron of aluminium, then the emission of electrons will be:

In the photoelectric effect,electrons are emitted from a metal surface only when the incident light has a certain minimum . . . . . . .

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A :$ In photoelectric effect,on increasing the intensity of incident light,the stopping potential increases.
Reason $R :$ Increase in intensity of light increases the rate of photoelectrons emitted,provided the frequency of incident light is greater than threshold frequency.
In the light of the above statements,choose the correct answer from the options given below:

The value of the stopping potential in the following diagram is ......... $V$.

Do all the electrons that absorb a photon come out as photoelectrons?

Threshold wavelength for photoelectric emission from a metal surface is $5200\,\mathring{A}$. Photoelectrons will be emitted when this surface is illuminated with monochromatic radiation from: