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The number 6.022 × 1023 indicating the number of atoms or molecules in a mole of any substance
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Hello!</h2>
The answer is:
The empirical formula is the option B. 
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Why?</h2>
The empirical formula of a compound is the simplest formula that can be written. On the opposite, the molecular formula involves a variant of the same compound, but it can be also simplified to an empirical formula.

We are looking for a formula that cannot be simplified by dividing the number of molecules/atoms that conforms the compound.
Let's discard option by option in order to find which formula is an empirical formula (cannot be simplified)
A. 
It's not an empirical formula, it's a molecular formula since it can be obtained by multiplying the empirical formula of the same compound.

B. 
It's an empirical formula since it cannot be obtained by the multiplication of a whole number and the simplest formula. It's the simplest formula that we can find of the compound.
C. 
It's not an empirical formula, it's a molecular formula since it can be obtained by multiplying the empirical formula of the same compound.

D. 
It's not an empirical formula, it's a molecular formula since it can be obtained by multiplying the empirical formula of the same compound.

Hence, the empirical formula is the option B. 
Have a nice day!
The correct answer among the choices given is the first option.The teacher most likely is talking about distillation of a mixture. Distillation is a unit operation that separates component substances from a liquid mixture which is shown by the teacher. Also, the most common purifying technique in the production of gasoline is by this process.