Question

which of the following orbitals are allowed and not allowed in an atom?
2s,2d,3f,4f,6g

Answer 1

2s,4f are allowed while others are not and 6g is not any orbital 

You can solve this by simply remember (n+l) formula 
for 
 orbital  Value of l
   s           0
   p           1
   d           2
   f            3
and n is the coefficient in term i.e. 2s have n=2 and l=0
for s n+l starts from 1
for p it starts from  3
for d it is 5
and for f it is 7 
So if the value of (n+l) is in the range given above then it is valid orbital

Answer 2

Explanation:

2d is right answer....