Question

Number of nucleons in the nucleus is called
A. Mass number
B. Atomic number
C. Neutron number
D. Electron number

Answer 1

Hint: Nucleons are the subatomic particles that reside inside the nucleus of an atom. Recall the definition of each given option. The mass number is the sum of the number of protons and neutrons. The atomic number is the number of protons.

Complete answer:
Let’s define what nucleons are. The nucleons are the subatomic particles that reside inside the nucleus. We know that the two subatomic particles that are protons and neutrons reside inside the nucleus of an atom while the electrons revolve around the nucleus.

To answer this question, let’s check every option one by one as follows: We denote the mass number of the atom by the letter A. It is the sum of total number of protons and total number of neutrons contained by the atom. Therefore, $$\text{mass number}=\text{number of protons}+\text{number of neutrons}$$
Therefore, the option A is correct.

We denote every element by its atomic number. The atomic number of the element is the net charge on the nucleus of the atom. Since the neutrons are charge less particles, the charge on the nucleus is due to the number of protons in the atom. Therefore, the atomic number is equal to the number of protons in the atom. Thus, the option (B) is incorrect.

We know that the neutron number is the number of neutrons in the nuclide. But the nucleon is the sum of the number of protons and number of neutrons. Therefore, the option C is incorrect.

The electron number is equal to the atomic number of the element. Therefore, we can see the electron number cannot be the number of nucleons. Thus, the option D is incorrect.

Hence, the correct answer is option A.

Note: Every element has its atomic number and mass number. Since the mass number is the sum of both protons and neutrons in the nucleus and the atomic number is equal to the number of protons, the mass number is usually twice the atomic number. However, some of the elements may have different mass numbers for a given atomic number. This is called isotopes of the element.