Which of the following is not a correct ionic formula unit?
select one:
a. bao
b. ca₃n₂
c. kcl
d. lis₂

The answer to your question is letter d) LiS₂

Explanation:

Ionic compounds are composed by a metal and a non metal element, so all the formulas in this question are ionic, so we need to check the valences are correct.

a. BaO   this formula is correct because Ba has a valence of 2 and O also has a valence of 2, as the valences are the same, we do not write them.

b. Ca₃N₂   this is correct because Ca has a valence of 2 and N has a valence of 3, so we cross the valences to write the formula and we get what is written.

c. KCl  This formula is correct, K has a valence of 1 and Cl also has a valence of 1, then we do not write them.

d. LiS₂ This formula is incorrect because Li has a valence of 1 and S has a valence of 2, when we cross then we get Li₂S, and not  LiS₂.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)