Answer:
there must be free-moving electrons in a compound to conduct electricity.
in solid ionic compounds, there are no free electrons so it can't conduct electricity.
But in aqueous form the forces of attraction are broken and the ions (cations and anions) are free to move. This means there are free electrons that allow the aqueous compound to conduct electricity.
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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!
Explanation:
Atoms never gain protons; they become positively charge only by losing electrons. A positive ion is called a cation (pronounced: CAT-eye-on). You may have notice that the number of neutrons in each of these ions was not specified.