An element ‘M' has 50% of the electrons filled in the 3rd shell as in the 2nd shell. Theatomic number of ‘M’ is:

The atomic number of an element is equal to the number of protons in its nucleus, which is also equal to the number of electrons in a neutral atom.

The 2nd shell of an atom can hold up to 8 electrons (2 in the 2s subshell and 6 in the 2p subshell).

According to the problem, 50% of the electrons in the 3rd shell are equal to the number of electrons in the 2nd shell. This means that the 3rd shell has half the number of electrons as the 2nd shell, so it has 4 electrons (50% of 8).

The 1st shell can hold up to 2 electrons.

So, if we add up the electrons in the 1st, 2nd, and 3rd shells, we get 2 (from the 1st shell) + 8 (from the 2nd shell) + 4 (from the 3rd shell) = 14 electrons.

Therefore, the atomic number of element 'M' is 14.