Compound X weighing 188.1 grams contains 98.1 g of zinc, 18.0 g of carbon, and the rest as oxygen. What is the percent composition of zinc?

1.

(98.1 g zinc) / (188.1 g) = 0.52153 = 52.2% zinc by mass

So answer b.

2.

(98.1 g Zn) / (65.380 g Zn/mol) = 1.5005 mol Zn

(18.0 g C) / (12.01078 g C/mol) = 1.4987 mol C

(188.1 g - 98.1 g - 18.0 g) / (15.99943 g O/mol) = 4.5002 mol O

Divide by the smallest number of moles:

(1.5005 mol Zn) / 1.4987 mol = 1.001

(1.4987 mol C) / 1.4987 mol = 1.000

(4.5002 mol O) / 1.4987 mol = 3.003

Round to the nearest whole numbers to find the empirical formula:

ZnCO3

So answer b.

[As a practical matter that is also the molecular formula, but not enough information is given in this question to prove it.]