There are n sub shells will be present in a principal energy level where n is principal quantum number.

Eg.: for n = 1; there is only one subshell i.e., I = 0

for n = 2; there are two subshells i.e., I = 0,1

Eg.: for n = 1; there is only one subshell i.e., I = 0

for n = 2; there are two subshells i.e., I = 0,1