Question

Which of the following pairs are isotopes?
A) Oxygen and ozone
B) Ice and steam
C) Nitric oxide and nitrogen dioxide
D) Hydrogen and deuterium

Answer 1

Hint: We need to remember that isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei.

Complete answer:
We will look at all the options to answer this question:
Option A) oxygen and ozone are not isotopes of each other since in oxygen there are two atoms of oxygen while in ozone there are three atoms of oxygen. While isotopes are the one having the same atomic number but different mass number in this case both are different.
Option B) this option is incorrect as ice and steam are not isotopes of each other but they are two different forms of water that differ in the physical states of the matter.
Option C) this option is incorrect as both are having different chemical formulas thus they cannot be isotopes.
Option D) this option is correct as hydrogen and deuterium are isotopes of each other since they have the same atomic number but different mass number.
\[^2H{,^1}H\]

Option D is the correct answer.

Note:
We must have to know that hydrogen has no neutrons, deuterium has one, and tritium has two neutrons. The isotopes of hydrogen have, respectively, mass numbers of one, two, and three. Their nuclear symbols are therefore $1H$, $2H$ and $3H$. The atoms of these isotopes have one electron to balance the charge of the one proton.