Question

The isotope deuterium of hydrogen has
A. no neutron and one proton
B. One neutron and two protons
C. One electron and two neutron
D. One proton and one neutron

Answer 1

The chemical elements that have a different number of neutrons are known as isotopes. Hydrogen has three isotopes. Hydrogen, deuterium, and tritium. The mass number of hydrogen is one. The mass number of deuterium is two and the mass number of tritium is three.

Complete answer:
An element has three subatomic particles, protons, electrons, and neutrons. The proton number is known as the atomic number of an element. For every element, the atomic number is fixed and unique.
The species that have the same number of protons but a different number of neutrons are known as isotopes.

Hydrogen has one proton and one electron. Hydrogen does not have neutrons.The second isotope of hydrogen is deuterium. Deuterium has one proton, one electron, and one neutron.The third isotope of hydrogen is tritium. Tritium has one proton, one electron, and two neutrons.

All isotopes are shown as follows:
$_{\text{1}}^{\text{1}}{\text{H}}$, $_{\text{1}}^2{\text{D}}$, $_{\text{1}}^3{\text{T}}$
So, the isotope deuterium of hydrogen has one proton and one neutron.

Therefore, option (D) one proton and one neutron is the correct answer.

Note: The isotopes have the same number of the proton but different mass number due to different neutron numbers. Due to the same proton number, isotopes represent the same element. The mass number is determined as the sum of proton and neutron numbers. So, the mass number of hydrogen is one. The mass number of deuterium is two (one proton and one neutron). The number of electrons is also the same in all isotopes.