Define the following 1)atom 2)atomic number 3)valency
Atom: the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.
Atomic number:the number of positive charges or protons in the nucleus of an atom of a given element, and therefore also the number of electrons normally .
valency: The capability of an atom to gain or lose it valence electrons in order to complete it's valence shell ( last shell) is known as valency . Or the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.
Above given both definition are correct u can write whichever one u want...Hope u do well in exams cheers!!