The percent of sodium (by mass) in the hydrate

1. Write the formula for the given compound.

2. Calculate the molar mass of each part of the compound separately. Also, the number in front of the water molecule must be distributed and multiplied by the subscript of both the hydrogen and the oxygen in the water molecule.

3. Add the totals for each part together to find the molecular formula mass.

4. Divide each part’s mass by the molecular formula mass.

5. Multiply each result by 100 in order to get a percentage.

Hope this helps

Ithink the answer is a or d.