Q.Match the following:
Element: a. $^{40}_{18}Ar$ b. $^{14}_{6}C$ c. $^{40}_{19}K$ d. $^{14}_{7}N$
No. of Neutron: i. 7 ii. 21 iii. 8 iv. 22

The atomic number, symbol Z, is the number of protons in an atom's nucleus, and it is what fixes the chemical identity of an element — every atom of the same element has the same Z. Since an atom is electrically neutral overall, and its positive charge comes entirely from Z protons, it must also carry exactly Z electrons outside the nucleus. The mass number, symbol A, is the TOTAL count of nucleons — protons plus neutrons — since protons and neutrons are the particles that contribute essentially all the measurable mass; the neutron count itself is written N. These three quantities are linked by $A = Z + N$, so $N = A - Z$. An atom's exact composition is written using th …