Why is the 2nd ionization energy of Aluminum higher than that of Silicon?

Question

According to the ionization energy periodic table trend, silicon's should be higher but its. 

Answer 1

Consider the subshell those second electrons have to leave. In Al⁺, you have to break into the full 3s subshell. In Si⁺, the electron configuration is 3s²3p¹, so you don't need to add extra energy to disrupt a completely filled subshell to kick off the next electron.