atom, smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.
An atom is a particle of matter that uniquely defines achemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons.
In a human diploid somatic cell (2n), there are 22 chromosomes present in two copies and 1 pair of sex chromosomes. This means there are 23 pairs of chromosomes - 22 pairs of autosomes and 1 pair of sex chromosomes. There are in total 46 chromosomes (23 pairs in 2 copies: 23 × 2 = 46).
