What is the formula mass of calcium sulfate dihydrate $\left[ CaSO _4 \cdot 2 H _2 O _{\text {] ? Be }}\right.$ sure to add the water of hydration, which is the $2 H _2 O$ part (water surrounding the calcium sulfate).
$136 g / mol$
$154 g / mol$
$164 g / mol$
$172 g / mol$