Which one among the following shows particle nature of light?

A photo-cell is illuminated by a source of light, which is placed at a distance d from the cell. If the distance become d/2, then number of electrons emitted per second, will be

X(n, $$\alpha $$) $${}_3^7$$Li, then X will be

The interplanar distance in a crystal is 2.8 $$ \times $$ 10^$$-$$8 m. The value of maximum wavelength which can be diffracted