Question

The sum of the number of neutrons and protons in the isotopes of hydrogen is:
(A) 6
(B) 5
(C) 4
(D) 3

Answer 1

Hint : The sum of the number of neutrons and protons is called the mass number. Hydrogen has three naturally occurring isotopes which are $^1H{,^2}H{,^3}H$ .

Complete Step By Step Answer:
Hydrogen has three isotopes, namely, Protium, Deuterium and Tritium.
Isotope Number of protons Number of neutrons
Hydrogen $1$ $0$
Deuterium $1$ $1$
Tritium $1$ $2$
The sum of the number of protons in the isotopes is, $1 + 1 + 1 = 3$ .
The sum of the number of neutrons in the isotopes is, $0 + 1 + 2 = 3$ .
Therefore, the sum of the number of neutrons and protons in the isotopes of Hydrogen is $3 + 3 = 6$ .
Hence, the correct option is A.

Note :
Hydrogen is the only element having different names for its isotopes. $^2H$ Isotope is called Deuterium and $^3H$ isotope is called Tritium. $D$ and $T$ are the symbols used for Deuterium and Tritium. The first two isotopes, that is, protium and deuterium are stable, while tritium has a half-life of $12.32$ years.
$^1H$ isotope is the most common isotope. It has an abundance of more than $99.98\%$ . It is considered as a stable isotope. The nucleus of the $^1H$ isotope contains only a single proton. It has no neutrons. Thus it is named as protium. It is considered a stable isotope because the proton has never been observed to decay.
$^2H$ isotope of deuterium contains one proton, one neutron and one electron in its nucleus. It is also a stable isotope. Deuterium is a potential fuel for commercial nuclear fusion. It is not radioactive. Water containing deuterium is called heavy water. The nucleus of deuterium is called deuteron.
$^3H$ isotope contains one proton, two neutrons and one electron in its nucleus. It is radioactive. It is used in thermonuclear fusion weapons. Because of the interaction of cosmic rays with atmospheric gases, trace amounts of tritium occur naturally.
Isotopes of an element have the same atomic number, not the same mass number. All isotopes of a given element of a given element have the same number of protons but different numbers of neutrons.