Question

The atomic number of an element is always equal to:
A. Number of neutrons in nucleus
B. Half of the atomic weight
C. Electric charge of the nucleus
D. Weight of the nucleus

Answer 1

Hint: The general definition of the atomic number is defined on the basis of number of protons present inside the nucleus of an atom. while if an atom is in neutral state it can also be equal to the number of electrons.

Step by step answer: The atomic number is the number of protons present in the nucleus of an atom. Every atom has a unique atomic number.
The atomic representation is as follows:
\[_{\text{Z}}^{\text{A}}{\text{X}}\]
\[{\text{X}}\]is the symbol of the atom.
\[{\text{Z}}\] is the atomic number of proton number.
\[{\text{A}}\]is the atomic mass.
Protons and neutrons are present in the nucleus and electrons are present in the orbital around the nucleus.
Atomic numbers combine with the number of neutrons to give the atomic mass of the atom. So, the number of atoms does not represent the atomic number so, option (A) is incorrect.
Neutrons are heavier than protons so half of the atomic weight cannot represent the number of the protons, so option (B) is incorrect.
The charge of a proton is positive and the charge of an electron is negative. The charge of neutrons is zero so, the charge of the nucleus is equal to the charge of the proton.
The charge of proton is $ + 1$ so, the total charge of the nucleus represents the number of protons and the number of protons which in turn represents the atomic number.
So, the total charge of the nucleus represents the atomic number.

So, option (C) is correct.

Note: The charge of the nucleus is positive due to the charge of the proton. The charge of the electron is negative. Neutron is neutral. The mass of the neutron is slightly more than the mass of the proton.