Question

In two elements ${}_{{{Z}_{1}}}{{A}^{{{M}_{1}}}}$ and ${}_{{{Z}_{2}}}{{B}^{{{M}_{2}}}}$ . ${{M}_{1}}\ne {{M}_{2}}$ and ${{Z}_{1}}\ne {{Z}_{2}}$ but ${{M}_{1}}-{{Z}_{1}}={{M}_{2}}-{{Z}_{2}}$ . These elements are
A. Isotonic
B. Isobaric
C. Isotopic
D. Isoprotonic

Answer 1

Hint: The elements which have same mass number are called as isobars, the elements which have same atomic number and different mass number are called isotopes, the elements which have same number of neutrons are called isotones and the elements which have same number of protons are called isoprotonic.

Complete Solution :
- In the question it is given that there are two elements A and B with atomic numbers Z1 and Z2 and with mass numbers M1 and M2.
- It is also given that their atomic numbers and mass numbers are not equal.
- But it is given that the difference between mass number and atomic numbers are the same.
(${{M}_{1}}-{{Z}_{1}}={{M}_{2}}-{{Z}_{2}}$).

- We know that the difference between mass number and atomic number of an element gives the number of neutrons present in it.
- Means from the question we can say that the elements A and B have same number of neutrons
(${{M}_{1}}-{{Z}_{1}}={{M}_{2}}-{{Z}_{2}}$) in it.

- If the elements have the same number of neutrons then they are called as isotones.
- Therefore the elements A and B are isotones.
So, the correct answer is “Option A”.

Note: The difference between the mass number and atomic number of an element gives the information about the number of neutrons present in the element.
- Number of neutrons in an element = Mass number of the element – Atomic number of the element
In an atom the atomic number is equal to the number of electrons present in the atom.