‘‘Atomic number of an element is considered to be a more appropriate parameter than its atomic mass for a chemist.’’ Take the example of the element X (atomic number 13) to justify this statement.

The atomic number is the number of protons whereas atomic mass is the sum of the number of protons and neutrons in the nucleus.

Atomic number increases regularly by one in going from one element to the next element but atomic mass does not vary regularly must of the chemical properties of elements depend upon valence electrons and electric configuration of an atom which in turn depends on the number of electrons i.e, atomic number. That's why the atomic number of an element is considered to be more appropriate than its atomic mass for a chemist.

Element X (Aluminium) having atomic number 13.

Electronic configuration - $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$

Valence electron of X (Al) = 3