Question

An atom Q has a total number of 12 electrons. Calculate the number of electrons in its outermost shell.

• A. 2

Answer 1

The correct option is A 2
According to Bohr-Bury scheme, the maximum number of electrons in an orbit is given by the formula: $2$ $\times$ $n^2$, where n is the orbit number.
Therefore the maximum number of electrons in:
K-shell = 2
L-shell = 8
M-shell =18

Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

Hence the 12 electrons will be distributed as follows:
K-shell = 2 electrons
L-shell = 8 electrons
M-shell = 2 electrons

Hence, the atom Q has 2 electrons in its outermost shell.