Question

an element can have items with different mass number but same chemical properties and some are also used in the field of medicine in the treatment of disease what are such element known as define define such elements and also write one example of which property are different in them

Answer 1

Atoms having same atomic number ((chemical properties) but different mass numbers are called isotopes.
Examples are Hydrogen ( Protium, deutrium, and tritium).
An isotope of iodine is used to test goitre.