Question

Which of the following elements has same number of protons, electrons and neutrons ?

• A. ${}_{13}{}^{27}\mathrm{Al}$
• B. ${}_{12}{}^{24}\mathrm{Mg}$
• C. ${}_{17}{}^{35}\mathrm{Cl}$
• D. ${}_{11}{}^{23}\mathrm{Na}$

Answer 1

The correct option is B

${}_{12}{}^{24}\mathrm{Mg}$

The correct option is (B).

Explanation of correct option:

1. An atom is represented by its symbol for the element. The atomic number is written on the lower side of the symbol and the mass number is written on the upper side.
2. Magnesium Mg (Z=12) has the12 number of protons, electrons, and neutrons respectively. And its mass number (A) is 24.$$\begin{gathered} \mathrm{Atomic}\mathrm{number}=\mathrm{number}\mathrm{of}\mathrm{proptons}=\mathrm{number}\mathrm{of}\mathrm{electrons}=8 \\ \mathrm{Mass}\mathrm{number}=\mathrm{number}\mathrm{of}\mathrm{protons}+\mathrm{number}\mathrm{of}\mathrm{neutrons} \\ \mathrm{Number}\mathrm{of}\mathrm{neutrons}=\mathrm{Mass}\mathrm{number}-\mathrm{number}\mathrm{of}\mathrm{protons} \\ \mathrm{Number}\mathrm{of}\mathrm{neutrons}=24-12 \\ =12 \end{gathered}$$
3. The electronic configuration of magnesium is 2,8,2.

Explanation of incorrect option:

Option (A): Aluminium Al (Z=13) has 13 protons, 13 electrons, and 14 neutrons. And mass number (A) of aluminium is 27.

Option (C): Chlorine Cl (Z=17) has 17 protons, 17 electrons, and 18 neutrons. The mass number (A) of chlorine is 35.

Option (D): Sodium Na (Z=11) has 11 protons, 11 electrons, and 12 neutrons. The mass number (A) of chlorine is 23.

Thus, ${}_{12}{}^{24}\mathrm{Mg}$ has same number of protons, electrons, and neutron.