Question

If an atom of an element has 34 electrons in total, then which orbit is the outermost orbit of the atom and how many valence electrons it contains?

• A. N, 26
• B. N, 6
• C. M, 26
• D. M, 2

Answer 1

The correct option is B

N, 6

The maximum number of electrons in each orbit are given by $2$ $\times$ $n^2$.
So,
$$\begin{array}{cc}\text{Orbit}& \text{Maximum no. of electrons}\\ \text{K}& \text{2}\\ \text{L}& \text{8}\\ \text{M}& \text{18}\\ \text{N}& \text{32}\end{array}$$

Filling of electrons takes place from inner orbit to outer orbit. 34 electrons can be distributed as follows:
K- 2 electrons
L- 8 electrons
M-18 electrons
After complete filling of K, L and M orbits remaining numbers of electrons i.e.34-(2+8+18)=6 are filled in orbit N.
Hence, N is the outermost orbit and number of valence electrons are 6.