Answer
B
Work Step by Step
Molar masses (g/mol): $BeCl_2: 79.92,\ MgCl_2: 95.21,\ CaS: 72.14$,
$SrCO_3: 147.63,\ BaSO_4: 233.39$
$BeCl_2$ is not ionic, so it doesn't have any ions.
$MgCl_2$ releases 3 ions when dissociating $1 Mg^{2+},\ 2Cl^-$, as opposed to the other ionic compounds which release 2.
$MgCl_3$: $1.0\ g\div95.21\ g/mol\times3=0.032\ \mbox{moles of ions}$
For the others, since the mass and the number of ions released per compound are the same the one with the largest number of ions is the one with the smallest molar mass: CaS.
CaS: $1.0\ g\div72.14\ g/mol\times2=0.028\ \mbox{moles of ions}$
Therefore, the answer is B.
