Question

Why alkali metals are photosensitive even to visible light?

Answer 1

Some alkali metals such as lithium, sodium, potassium, caesium and rubidium were sensitive even to visible light. All these photosensitive substances emit electrons when they are illuminated by light. After the discovery of electrons, these electrons were termed as photoelectrons.

Answer 2

alkali metals said to be most suitable for the photoelectric effect because the alkali metal have more and more tendency of loosing electrons and hence makes it easier for the photon to eject it out from the atom with the consumption of less energy.