Question

Which of the following describe two real two stable cations?
A. Ge 3+ and Ge 1+ E. Sb2+ and Sb4+
B. N+ and N3+ F. Don’t pick this one.
C. Sb3+ Sb5+ G. Li+ and Li3+
D. Tl2+ and Tl4+

Answer 1

Be sure to check the periodic table to determine how many valence electrons each type of element usually have.

The period(column) will tell you this number. Moreover you will need to deduce the amount of electron shells each type of element can have in order to achieve stability at a higher positive charge.

Unfortunately I don't remember exactly how to determine this(nor do I have time to do so), but this will give you a step in the right direction.