#### Answer

a) $C_5H_{12}$
b) $HgCl$
c)$CH_2O$

#### Work Step by Step

To obtain the empirical formula, we divide the subscripts by their greatest common factor.
a) for $C_5H_{12}$, the greatest common factor of the subscripts is 1. Thus, the empirical formula is $C_5H_{12}$
b) for $Hg_2Cl_{2}$, the greatest common factor of the subscripts is 2. So, the empirical formula is $HgCl$
c) for $C_2H_4O_{2}$, the greatest common factor of the subscripts is 2. So, the empirical formula is $CH_2O$