<u>Explanation:</u>
Empirical formula is defined as the formula in which atoms in a compound are present in simplest whole number ratios.
For the given options:
- <u>Option a:</u> Acetic acid
Acetic acid having molecular formula
. To write the empirical formula, we divide each subscript by 2.

Hence, the empirical formula for acetic acid is 
- <u>Option b:</u> Citric acid
Citric acid having molecular formula
. To write the empirical formula, we divide each subscript by 1.

Hence, the empirical formula for citric acid is 
- <u>Option c:</u> Hydrazine
Hydrazine having molecular formula
. To write the empirical formula, we divide each subscript by 2.

Hence, the empirical formula for hydrazine is 
- <u>Option d:</u> Nicotine
Nicotine having molecular formula
. To write the empirical formula, we divide each subscript by 2.

Hence, the empirical formula for nicotine is 
Butane having molecular formula
. To write the empirical formula, we divide each subscript by 2.

Hence, the empirical formula for butane is 