Question

Isotopes of an element have the same atomic number but a different ________.

• A. number of electrons
• B. valency
• C. number of protons
• D. mass number

Answer 1

The correct option is D mass number

Atoms that have same atomic number (number of protons) but different mass numbers (number of protons and neutrons) are called isotopes.
For example, mass numbers of carbon- 12 and carbon- 14 are 12 and 14 respectively, whereas atomic number for both of them is 6.