Which of the following will displace the halogen from the solution of the halide?
(A) $B{{r}_{2}}$ added to $NaCl$ solution
(B) $C{{l}_{2}}$ added to $KCl$ solution
(C) $KCl$ added to $NaF$ solution
(D) $B{{r}_{2}}$ added to $KI$ solution

Hint: Displacement reactions are those in which a part of one reactant is replaced by another reactant. There are two types of displacement reaction: Single displacement reaction and double displacement reaction. For an element to displace another element, it should have higher reactivity.

Complete Step by Step Solution:
The order of reactivity of halogens is: Fluorine > Chlorine > Bromine > Iodine

When $B{{r}_{2}}$ is added to $NaCl$ solution, the bromine will not displace chlorine as it is less reactive than chlorine. So, there will be no reaction. When $C{{l}_{2}}$is added to $KCl$ solution, there will be no change. When $KCl$is added to $NaF$ solution, chlorine will not displace fluorine as it is less reactive than fluorine. So, there will be no reaction.

When $B{{r}_{2}}$ is added to $KI$ solution, the bromine will displace iodine from potassium iodide to form potassium bromide. The reason for this is that bromine is more reactive than iodine.

Correct Option: (D) $B{{r}_{2}}$ added to $KI$ solution

Additional Information: The chemical reactivity of metals depends upon their position in the reactivity series. An element placed at a higher position can displace an element placed at a lower position. A cation always displaces a cation and an anion always displaces an anion.

Note: The halogens are very reactive species. This is because it contains seven electrons in the valence shell and thus requires only one electron to complete its octet.