Answer. Alkanes give only substitution reactions. These reactions are a characteristic property of alkanes. Alkanes react fairly with halogens in diffused sunlight only. In dark there is no reaction. In direct sunlight reaction is explosive and carbon is deposited.
CH4 + 2C12———> C + 4HC1
In diffused sunlight a series of reactions take place and in each step one hydrogen atom is substituted by halogen atom in four steps, all the hydrogen atoms are substituted one by one by halogen atoms
diffused
CH4 + C12 CH3C1 + HC1
Sunlight Chloromethane
CH3C1 + C12 CH2C12 + HC1
Dichloromethane
CH2C12 + C12 CHCl3 + HCl
Trichloromethane
(Chloroform)
CHC13 + C12 CCl4 + HC1
Tetrachloromethane
(Carbon tetrachloride)