Element A has an atomic number 12, element B has atomic number 15. The formula of the possible compound containing these elements is:
(A) \[AB\]
(B) \[A{B_2}\]
(C) \[{A_2}{B_3}\]
(D) \[{A_3}{B_2}\]

Hint: In order to determine the compound formed, we must know to write the electronic configuration of the atomic number given. With that electronic configuration you can find the valency of the element. This valency will help you to determine the compound which will be formed.

Complete answer:
Before going to the problem, let us first understand what an atomic number is. Atomic number is the number of protons that is present in the nucleus of an atom. Atomic number is denoted by Z. In the periodic table atoms are arranged in the increasing order of their atomic number.
It is given that element A has an atomic number, Z=12.
The electronic configuration of A is \[1{s^2}2{s^2}2{p^6}3{s^2}\].
Since the outermost orbital is 3s, it is a s block element. The outermost orbital 3s have two electrons in it. Hence, its valency is 2. The element A has to lose two electrons from the outermost orbital in order to obtain the nearest stable gas configuration, i.e. [ Ne] configuration.
Element B has an atomic number, Z=15.
The electronic configuration of B is \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}\].
As the outermost orbital of element B is 3p, it is a p block element. The outermost orbital has 2+3=5electrons. Hence, the valency of the p-block element is 5. It has to gain three electrons, in order to obtain the nearest stable gas configuration, i.e. is [Ar] configuration.
Therefore, \[{A^{2 + }}{B^{3 - }}\] will form \[{A_3}{B_2}\] compound.

Hence, the correct answer is option(D) \[{A_3}{B_2}\].

Additional Information:
What is a mass number? Mass number is the number of protons and neutrons present together in the nucleus. Protons and neutrons together are also called nucleons. Mass number is denoted by the symbol A. Mass number is usually used to distinguish between the isotopes of an element.

Note: Electronic configuration of an element will be given by following these rules.
-Pauli’s Exclusion principle: No two electrons in an orbital will have all the four quantum numbers equal.
- Hund’s rule: All the orbitals in a subshell should be singly filled, before any orbitals are doubly filled.
- Aufbau’s principle; The filling of the electron in the orbitals of an atom will takes place according to the increasing order of their energy.