Account for the following :
(a) White silver chloride turns grey in sunlight.
(b) Brown coloured copper powder on heating in air turns into black coloured substance.

Explanation

(a) Silver chloride turns grey on exposure to sunlight because of the following reaction :
`2AgCl overset("Sunlight")(to)underset("(grey)")underset("Metallic silver")(2Ag+Cl_(2))`
(b) Oxidation of copper powder takes place. The oxide formed has a black colour.
`underset("Brown")(2Cu)+O_(2)overset("Heat")(to)underset("Black")(2CuO)`