The atoms of different elements having same mass number but different atomic number are known as isobars.
The sum of protons and neutrons, in the isobars is always different.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false
D. If assertion is false but reason is true.

Answer

C

Explanation

( c) The assertion that the isobars are the atoms is different elements having same mass number but different atomic number, is correct but reason is false because atomic mass is sum of number of neutron and protons which should be same for isobars.