Question

A phosphorus atom has a total of 15 electrons. Its outermost shell is _____ and it has ___ valence electrons.

• A. L; 8
• B. L; 5
• C. M; 8
• D. M; 5

Answer 1

The correct option is D M; 5

According to the Bohr-Bury scheme, the maximum number of electrons present in a shell is given by ‘$2n^2$’.

Here n is denoted as the shell number.

• So, when K(n)= 1,

Maximum number of electrons ($2n^2$) = $2x{1}^2$ = 2

• So, when L(n)= 2,

Maximum number of electrons ($2n^2$) = $2x{2}^2$ = 8.

• So, when M(n)= 3,

Maximum number of electrons ($2n^2$) = $2x{3}^2$ = 18.


We know the atomic number of phosphorus is 15.

• K-shell = 2 electrons
• L-shell = 8 electrons
• M-shell = 5 electrons (outermost shell)