The answer is: S,P,D,F. Beyond F they follow normal alphabetic order: G, H, I, etc.
Energy Level: Sublevels
1: s
2: s, p
3: s, p, d
4: s, p, d, f
5: s, p, d, f, g
6: s, p, d, f, g, h
7: s, p, d, f, g, h, i
2s, 3p, 4s, 3d
S P D F
4p
Electron Configuration
There are 2 energy sublevels in the second principal.
There are two sublevels in the 2nd principal energy level. They are the 2s and 2p sublevels.
filled energy sublevels
3, three, tres
electrons occupy sublevels in the order of increasing energy .
Electron Configuration
The level of energy possessed by all electrons in one type of orbital
Each electron occupies the lowest energy orbital. Orbitals related to energy level are of equal energy.
There are 2 energy sublevels in the second principal.
There are two sublevels in the 2nd principal energy level. They are the 2s and 2p sublevels.
Sublevels
filled energy sublevels
3, three, tres
Depends on what one means by "smaller". Since sublevels are "inside" or part of the principle energy level, then yes, they are smaller.
There are five sublevels in the fifth energy level: 5s, 5p, 5d, 5f, and 5g.
In krypton atoms, the 3s and 3p sublevels are filled, i.e. 3s23p6.