Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens. Particular substances have been linked to specific types of cancer. Tobacco smoking is associated with many forms of cancer, and causes 90% of lung cancer.
Human diploid cells have 46 chromosomes and human haploid gametes (egg and sperm) have 23 chromosomes. Retroviruses that contain two copies of their RNA genome in each viral particle are also said to be diploid.
However, your germ cells (sperm in males and egg in females) have half the number of chromosomes in your somatic cells (the cells of the body other than the germ cells), that is 23 chromosomes. This is because 23 from the sperm + 23 from the egg= 46 in the zygote = 46 in the adult human. This halving from 46 to 23 chromosomes is made possible by a process termed as meiosis.