Double displacement reactions usually occur in:

Correct option is A

Correct option: (a), aqueous solution

Double displacement reactions usually occur in aqueous solutions where two compounds in solution react to form two new compounds, typically resulting in the formation of a precipitate, a gas, or water.

A general representation of a double displacement reaction is:

$$AB + CD \rightarrow AD + CB$$ 

AB and $CD$ are two ionic compounds.

The ions in the reactants swap partners to form two new compounds, $AD$ and CBCBCB.

Information Booster: 

1. Precipitation Reactions: When two aqueous solutions combine to form an insoluble product (precipitate). For example:

$$AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$$ 

Here, silver chloride (AgCl) forms as a precipitate.

2. Neutralization Reactions: When an acid and a base react to form water and a salt. For example:

$$HCl(aq) + NaOH(aq)+ H_2O(l)$$ 

3. Gas Formation: In some reactions, a gas is formed. For example:

$$Na_2SO_3 (aq) +HCl (aq) \rightarrow NaCl(aq) + SO^2 (g) +H^2O(l)$$  

Here, sulfur dioxide (SO₂) is released as a gas.