Question

The value of A for a neutral atom is 25 and Z is 12; find the number of protons, neutrons and electrons in the atom.

• A. 12, 25 and 12 respectively
• B. 25, 12 and 25 respectively.
• C. 12, 13 and 12 respectively
• D. 12, 25 and 25 respectively

Answer 1

The correct option is C

12, 13 and 12 respectively

The atomic number, Z (=12), is equal to number of protons. Also, number of electrons is also 12, as the atom is neutral. The number of neutrons, N= A (mass number)-Z (atomic number)

25-12= 13.

Mass number is the total number of neutrons and protons present in the nucleus. It's termed as the mass number as the mass of the 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.