The halide used widely in photography is

Silver halide or silver salt is mostly used in photographic films

Explanation:

Silver halide crystals in gelatin are coated onto a film base, glass or paper substrate. And when a sliver halide crystal is exposed to light (photons strike) it turned into a small speck of metallic crystal and these comprise the invisible or latent image which is developed afterwards.

here we know that ball will drop down by total distance 3.2 m

so here we know that

now using kinematics

now in the same time it will cover horizontal distance of 0.75 m

so speed of the ball will be