Here's why:

* Electron Configuration: Aluminum has an electron configuration of 1s²2s²2p⁶3s²3p¹.

* Shell Structure:

* The first shell (n=1) can hold up to 2 electrons (1s²).

* The second shell (n=2) can hold up to 8 electrons (2s²2p⁶).

Therefore, the second shell of aluminum contains 2 (2s²) + 6 (2p⁶) = 8 electrons.