Question

The atomic number of magnesium is 12. The number of protons in the nucleus of magnesium atom is:
(A) 6
(B) 10
(C) 12
(D) 24

Answer 1

Hint: The atomic number is equal to the number of electrons present in the atom and the number of protons is equal to the number of electrons. The mass number is equal to the sum of the number of protons and neutrons.

Complete step by step answer:
-We know that an atom is made up of mainly three types of particles: the electrons, the protons and the neutrons. The electrons are negatively charged particles, while the protons are positively charged and neutrons are neutral particles. The nucleus of an atom is composed of protons and neutrons while the electrons revolve around the nucleus.
Also ideally atoms are neutral and for this the number of protons are equal to the number of protons.
-Now we will see how to calculate the number of protons, electrons are neutrons in an atom.
The atomic number of an atom is = The number of electrons present in it.
The number of electrons = The number of protons
Mass number = Number of protons + Number of neutrons
-Now we will talk about the number of protons, electrons and neutrons present in a magnesium atom. Magnesium has an atomic number of 12 and mass number of 24. It is represented as: ${}^{24}M{g}_{12}$
Since we know that: Atomic number = Number of electrons
So, for Mg: Number of electrons = 12
Since, the number of protons = number of electrons
For Mg: Number of protons = 12
Also, mass number = number of protons + number of neutrons
 Number of neutrons = mass number – number of protons
 = 24 – 12
 = 12
Hence we can say that the number of protons in the nucleus of a magnesium atom are 12.


The correct option is: (C) 12


Note: If two atoms have the same atomic number but different mass numbers, they are known as isotopes. If two atoms have the same mass number but different atomic numbers, they are known as isobars. If two atoms have the same number of neutrons, they are known as isotones.