Question

Boron occurs naturally as two isotopes. What is the difference between these isotopes?

Answer 1

d) They have different numbers of neutrons and different mass numbers.  Remember mass number is protons plus neutrons. The number of protons for an element will never change, however the number of neutrons can.

Answer 2

Atoms are made of 3 types of subatomic particles that are electrons, protons and neutrons.
the number of protons in the atom is called the atomic number. the atomic number is characteristic of the element.
the mass number is the sum of the number of protons and neutrons. Since protons and neutrons both have similar masses and they are located in the nucleus, the mass of the atom is the sum of protons and neutrons.
Isotopes are when 2 atoms of the same element have different number of neutrons. Therefore atomic number is the same but mass number is different as the number of neutrons vary.

correct answer for the difference between isotopes is 
d)They have different numbers of neutrons and different mass numbers.