Why is it possible to use physical properties to separate a mixture?

c. fluorine

Explanation:

A single replacement reaction is defined as the chemical reaction in which a strong molecule replaces the weak molecule from a compound.

In a single replacement reaction, the chloride ion in NaCl can be replaced     by fluorine and gives Sodium fluoride as fluorine (F) is stronger than chlorine (Cl) and from other given molecules also. So the single replacement reaction between NaCl and F will be:

NaCl + F2 => NaF + Cl2

Hence, the correct answer is "c. fluorine".