Question

Plz explain me this equation. How we can find that element is positive or negative ? eg.here Al3+,O2- plz explain the signs.

Answer 1

Here,

The ion Al3+ is a cation. Means that it has 3 positive charges i.e. 3 electrons are donated by aluminium.

The ion O2- is an anion. Means that it has 2 negative charges i.e. 2 electrons are accepted by oxygen.