Give the empirical formula for each of the following compounds if a sample contains:

(a) 0.0130 mol C, 0.0390 mol H, and 0.0065 mol O

(b) 11.66 g iron and 5.01 g oxygen

(c) 40.0% C, 6.7% H, and 53.3% O by mass

(d) 87.5% N and 12.5% H by mass