Which is true about the stopping potential vstop?

(a) it is the amount of energy required to stop an incident photon.
(b) it is the amount of energy required to stop a freed electron.
(c) the product of charge e and vstop is the amount of energy required to stop an incident photon.
(d) the product of charge e and vstop is the amount of energy required to stop a freed electron.

d

Explanation:

When a photon strikes a metal plate with an energy above the work function of the metal plate then outer orbit electrons will absorb the energy and escapes out of the metal plate.

After releasing electron is free to move in any direction without interacting with air molecules. Electron posses some kinetic energy and if we want to stop electron from moving in a particular direction then we have to apply an electric opposite to the direction of moving electron to cease its motion.

The Product of charge and Potential i.e. stopping potential will give the amount of energy required to stop the moving electron.

the independent variable, or the one that is intentionally manipulated is the speed.