Question

The atomic mass 25 and 13 neutrons in its nucleus. What its ions will be:
A. ${\text{M}}{{\text{n}}^{2 + }}$
B. ${\text{C}}{{\text{r}}^{ + 3}}$
C. ${\text{A}}{{\text{l}}^{ + 3}}$
D. ${\text{M}}{{\text{g}}^{2 + }}$

Answer 1

Hint: The nucleus of an atom consists of neutrons and protons. The mass of the atom is considered equal to the mass of the nucleus as the mass of electrons is negligible in comparison to the mass of protons.

Complete step by step answer:
We know that the atomic mass of an atom is equal to the sum of the protons and neutrons of the atom.
We are given the atomic mass and the number of neutrons in the nucleus of the atom.
So, we can find the number of protons of the element by subtracting the above quantities, that is, Number of protons = Atomic mass – number of neutrons $ = 25 - 13 = 12$.
Thus, we can conclude that, atomic number of the given element is 12.
We know that atomic number 12 is the element Magnesium $\left( {Mg} \right)$.
Magnesium has 2 electrons in its valence shell. Thus, it loses two electrons to form ${\text{M}}{{\text{g}}^{{\text{2 + }}}}$ ion.

Therefore, the correct answer is D.

Note:
An Atom of each element contains a fixed number of protons. Rather, we can say that the number of protons determines the atom we are considering. We are familiar with the fact that the number of protons in an atom is called the atomic number of the atom. Unlike the number of protons, the number of neutrons for a certain element can vary. Atoms of the same element that differ only in the number of neutrons in their nucleus are called isotopes. Together, the number of protons and the number of neutrons determine the atomic mass of the element.