This problem requires that you know nomenclature, to identify the formula of the compond from its name, and the way how to determine the formula mass once you know formula.
1) Nomenclature: Chromate
Chromate is an ion (anion) from the chromic acid.
Chromic acid is formed from Chromic oxyde with the atomic number 6.
Then Cr + O2 -> Cr2O6 = CrO3
CrO3 + H2O -> H2CrO4
H2CrO4 = 2H(+) + CrO4 (2-) <---- this is the ion chromate
Now you have to join the chromate ion with the sodium ion => Na2 (CrO4)
2) Now you can calculate the molar mass of the formula Na2(CrO4).
You must only muliply every subscript times the atomic mass of the element:
Na2 => 2 * 23 g/mol = 46 g/mol
Cr => 52 g/mol
O4 => 4 * 16g/mol = 64 g/mol
Formula mass = 46 g/mol + 52 g/mol + 64 g/mol = 162 g/mol
I used the numbers with less significant figures thant the problem required but the answer is evident. Also, g / mol = a.m.u = atomic mass unit.
