Question

The number of protons and neutrons for most stable element is:
(A) even-odd
(B) even-even
(C) odd-odd
(D) odd-even

Answer 1

An element is generally characterised by the stability of its nucleus, if the nucleus is stable then we can say the element or the atom is stable, therefore for that, we have to take into account the nuclear stability of that atom.

Complete step-by-step answer: All the nuclei are made of $2$ basic entities- neutrons and protons. Neutrons and protons have almost the same size but different electrical charges. The difference in mass between a neutron and proton is very small. Neutrons are electrically neutral and contribute only to the mass of the nucleus while a proton is a positively charged entity that is equal in strength to the negative charge possessed by an electron. When there is an even number of protons and neutrons in a nucleus, the spin-up protons and neutrons can pair off with the spin-down protons and neutrons. This interaction between the protons and neutrons makes the nucleus hold more tightly, lowering its net energy and making it more stable. The elements having an even number of protons and neutrons are very abundant, more stable, and richer in isotopes. Generally, due to this the nuclear stability is higher for nuclides that have even numbers of protons and neutrons or both in them.

Therefore, the number of protons and neutrons for most stable elements is even-even. Hence, option (B) is correct.

Note: The number of protons present in a nucleus is called the atomic number of that element. It is denoted by $Z$. The total number of neutrons and protons when combined together in a nucleus comprises the mass number of the atom.