Two compounds are considered as isomers if they have
a) same molecular formula or same structure
b) different molecular formula and same structure
c) same molecular formula and same structure
d) different molecular formula and different structure

In chemistry, isomers are compounds that have the same molecular formula but may differ in structure. This is common in the orientation of sugars. The answer is not in the choices.

The correct one should be same molecular formula, different in chemical structure.

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts

Sorry i dont understand the question can you rephase it?