There are 7 electrons on the third energy level
Further explanation
The maximum number of electrons that can be filled in the nth electron shell is 2n²(n=shell)
• K shell (n = 1) maximum 2 x 1² = 2 electrons
• L shell (n = 2) maximum 2 x 2² = 8 electrons
• M shell (n = 3) maximum 2 x 3² = 18 electrons
• N shell (n = 4) maximum 2 x 4² = 32 electrons
Electron configuration of Si : 1s²2s²2p⁶3s²3p⁵ = 17 electron
The electron distribution :
K shell(n=1) ⇒the first energy level= 2
L shell(n=2) ⇒the second energy level= 8
M shell(n=3)⇒the third energy level = 7