Question

A neutral atom has an atomic mass of 12 and has 6 neutrons. Find how many electrons, protons and shells are present in this atom.

Answer 1

Atomic mass of the atom = 12. Hence, the sum of protons and neutrons = 12
Since, there are 6 neutrons in the atom, no. of protons = 12 - 6 = 6

As stated in the question, the atom is neutral. So the total positive charge is equal to the total negative charge.
or, the no. of electrons = no. of protons = 6

Since the first shell can hold only 2 electrons, these 6 electrons will be accomodated in the K and L shells. Hence the atom has 2 shells.