Describe the substitution reaction of alkanes with chlorine as a photochemical reaction, with ultraviolet light providing the activation energy, ( E_a ), and draw the structural or displayed formulae of the products, limited to monosubstitution

Describe the Group VII halogens, chlorine, bromine and iodine, as diatomic non-metals with general trends down the group, limited to: (a) increasing density (b) decreasing reactivity