Question

The value of A for a neutral atom is 25 and Z is 12. Then, the number of protons and neutrons in the atom areand respectively.

• A. $12$
• B. $25$
• C. $13$
• D. $30$

Answer 1

Answer: (A), (C)

The correct options are
A $12$
C $13$

The atomic number, $(Z=12)$, is equal to the number of protons. Also, the number of electrons is $12$, as the atom is neutral.
Mass number is the total number of neutrons and protons present in the nucleus. The mass of an atom is almost equal to the sum of masses of neutrons and protons only as electrons are comparatively very light.
Mass number = number of protons + number of neutrons.
Therefore, number of neutrons = A(mass number) - Z(atomic number)
= $25-12=13$