Answer:
When n = 3 , l = 0 ≤ ℓ ≤ n − 1 that is 0,1,2
l = 0 , m =0, 1(s orbital)
l =1, ml = -1,0,+1 3 (px,py,pz orbitals)
l = 2 , ml = -2,-1,0,+1,+2 5 (dxy,dyz,dzx,dx2,dx2-y2)
There is 1 orbital for l = 0, 3 orbitals for l = 1, 5 orbitals for l = 2.
So, 1 + 3 + 5 = 9 orbitals are allowed for n = 3
