Answer :

3 C3H8O
because you cannot divide the subscripts anymore. The molecular formula is in it's simplest form. And C3H8O is a molecule as well. 

Answer : The correct option is, (3) [tex]C_3H_8O[/tex]

Explanation :

Empirical formula : It is defined as the simplest or most reduced ratio of atoms in a compound.

Molecular formula : It is defined as the how many atoms of each element present in a compound.

From the given options, the option (3) [tex]C_3H_8O[/tex] formula represent both a molecular and an empirical formula.

From [tex]C_3H_8O[/tex] formula, we can determine the molecular formula by multiplying the whole numbers (1, 2, 3, 4 ....etc.)

While the other options, (1), (2) and (4) do not represent both a molecular and an empirical formula. Only represent the molecular formula.

The molecular formula of Glucose is, [tex]C_6H_{12}O_6[/tex] and the empirical formula will be, [tex]C_1H_2O_1[/tex]

The molecular formula of Ethanoic acid is, [tex]C_2H_4O_2[/tex] and the empirical formula will be, [tex]C_1H_2O_1[/tex]

The molecular formula of Butene is, [tex]C_4H_8[/tex] and the empirical formula will be, [tex]C_1H_2[/tex]

Hence, the formula represent both a molecular and an empirical formula is, [tex]C_3H_8O[/tex]