Question

A dipositive ion has an electronic arrangement is $2,2,8.$ Find out the number of electrons, protons and neutrons in that element if its mass number is 40.

Answer 1

Hint: Dipositive ions: - Ions are charged species carrying both positive and negative charges. The dipositive ions are the ion carrying two units of positive changes. For example: calcium ($C{{a}^{2+}}$), magnesium ($M{{g}^{2+}}$).

Complete step by step answer:
First we will describe about the structure of atom,
Atoms are the smallest part of elements. Basic structure of an atom includes a tiny, relatively massive nucleus. Atoms consist of three particles: electrons, protons and neutrons.
Some symbol can be used to describe the element like atomic number (at the bottom) and mass number (at the top),
Atomic number is defined as the total number of protons present in the nucleus of an atom.
Z (atomic number) = number of proton (p) = number of electron (e)
Mass number is defined as the total number of protons and neutrons present in the nucleus of the atom.
A (mass number) = number of proton (p) + number of neutron (n)
Now according to the question,
The electron arrangement of dipositive ions = 2, 8, 8
That means, number of electrons in dipositive ions = 2+8+8=18
If the mass of the element = 40 I.e. Calcium
And due to dipositive ions, it is $C{{a}^{2+}}$= 20 (number of electron in dipositive ions)
Because number of electron = number of proton that means,
Number of proton = 20
So number of proton will be 20 and number of neutron will be
Number of neutron = mass number – number of proton
N = 40 -20 =20
Therefore, the number of protons, electrons and neutrons in the element are 20, 20, and 20.
Therefore, B is the correct option.

Note:
Alkaline earth metal always forms a dipositive ions like $C{{a}^{2+}},M{{g}^{2+}}$ because the compounds with +2 oxidation state have more lattices enthalpy. Alkaline earth metals are considered in s-block elements.