Which symbol represents a particle with a total of 10 electrons?
(1) n (3) al
(2) n3+ (4) al3+

Our  Al3+

Let me tell you why. Since this has 13 protons, we already know that when an atom is positive (ionic), means that it lost electrons. Since they have a 3+, we know that it lost 3 electrons.  

Protons = 13
Electrons usually equal the amount of protons, but it lost three in this case, so we subtract 3 from 13.

13 - 3 = 10

Now, we know that it has 10 electrons.