Understand that the incidence of mutations can be increased by exposure to ionizing radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).
Mutation is the change in base sequence of the genes which creates new alleles. (e.g. ACT => AAT)
Radation - Xrays or sunshine (UVB) in this case of UVB this can cause a mutation which leads to skin cancer
Chemicals - effects of tars and tobacco which causes a change in the base sequence which can also lead to cancer.
Chemicals which cause mutation are called mutagens and those that cause cancers are called carcinogen.