Which contains the greatest number of bromide ions?

Question

a) 100 mL of 1.0 M BaBr2
b) 50 mL of 2.0 M NaBr
c) 20 mL of 2.5 M FeBr3
d) All contain the same number of chloride ions.

How would I go about this question?

Answer 1

If you want a "complete" answer,
1. determine mols of Br for each from
mols = M x L
2. Multiply mols x 6.02E23
3. Compare to determine the one with the greatest.
OR
recognize that all will be multiplied by 6.02E23 which means #1 and #3 will answer the question.
a. is 1.0 M x 0.100 L x 2 Br/1 mol BaBr2
b. is 2.0 M x 0.050 L x 1 Br/1 mol NaBr.
c. is 2.50 M x 0.020 L x 3Br/1 mol FeBr3.
d. is an imaginary answer; there are no Cl ions in the problem.
Technically there are two answers; i.e., one answer is either a,b, or c but d is correct, too, because there are no Cl ions in any of the solutions.