Answer:
The answer is in the problem
Explanation:
As general rule of number of oxygen is -2:
O → -2
Alkali metals (Li, Na, K) are always +1
Na → +1
Alkali earth methals (Be, Mg, Ca...) are always +2
Ca → +2
The halogen group (F, Cl, Br...) is always -1
F → -1
The oxidation number of Si (+/- 4)
Aluminium is, usually +3
And to complete the octet rule in nitrogen, 3 electrons are required. That means:
N → -3
