Question

Which pair below describes isotopes of the same element?

Answer 1

Answer: The correct answer is Option B.

Explanation:

Isotope is defined as the chemical specie which belong to the same element but differ in their molecular mass.

The isotopes have same atomic mass but differ in their mass numbers

Atomic number is defined as the number of protons or electrons that are present in a neutral atom.

Atomic number = number of protons = number of electrons

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Thus, isotopes of an element has same number of protons but they differ in the number of neutrons.

For Example: Chlorine has 2 isotopes, $_{17}^{35}\textrm{Cl}\text{ and }_{17}^{37}\textrm{Cl}$

• In $_{17}^{35}\textrm{Cl}$ isotope:

Number of protons = 17

Number of neutrons = 35 - 17 = 18

• In $_{17}^{37}\textrm{Cl}$ isotope:

Number of protons = 17

Number of neutrons = 37 - 17 = 20

Hence, the correct answer is Option B.

Answer 2

B because isotopes have the same number of protons but a different number of neutrons