Question

Isotopes of an element contain

• A. the same number of protons but different number of neutrons
• B. the same number of neutrons but different number of protons
• C. equal number of protons and electrons
• D. equal number of nucleons

Answer 1

Answer: (A)

the same number of protons but different number of neutrons

Isotopes of an element must have same atomic number $\left(Z\right)$ but different mass number $A$.

Number of protons is equal to the atomic number.

So, isotopes of an element have same number of protons.

Mass number is equal to the sum of number of protons and neutrons i.e. $A=p+n$

Asisotopes of an element have different mass number but same number of protons, thus they must have different number of neutrons.