Question

If D+2 would react with E-1, what do you predict the formula to be. A) DE B)D2E C)DE2 D) D2E2

Answer 1

All you need to do the cross the charges and put it as suffixes. 

D+2 + E-1 ----> DE2

answer is C

Answer 2

Answer: C) $DE_2$

Explanation:

For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.  

Here D is having an oxidation state of +2 called as $D^{2+}$ cation and E $E^{-}$ is an anion with oxidation state of -1. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral $DE_2$.

The cations and anions being oppositely charged attract each other through strong coloumbic forces and form an ionic bond.