Name three isotopes of hydrogen, give their symbols, number of protons and number of neutrons.

Isotopes: Atoms of the same element that have same atomic number but different mass number.

• Example: Isotopes of element Hydrogen as given below:

Atomic number of Hydrogen (H) = 1

Symbol of any element (say X) is represented along with atomic and mass number as ${}_{\mathrm{Atomic}\mathrm{number}}{}^{\mathrm{Mass}\mathrm{number}}\mathrm{X}$

• Atomic number= Number of protons, therefore number of protons for all the isotopes of Hydrogen= 1
• Mass number= Number of protons +Number of neutrons
• Therefore, Number of neutrons= Mass number- Number of protons

S. No.	Isotope	Symbol	Representation	Number of protons	Mass number	Number of neutrons (Mass number- Number of protons)
1	Protium	P	${}_1{}^1\mathrm{H}$	1	1	1- 1= 0
2	Deuterium	D	${}_1{}^2\mathrm{H}$	1	2	2- 1= 1
3	Tritium	T	${}_1{}^3\mathrm{H}$	1	3	3- 1= 2