In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:

(A) exchange of atoms takes place

(B) exchange of ions takes place

(C) a precipitate is produced

(D) an insoluble salt is produced

The correct option is:

The reaction between sodium sulphate and barium chloride is represented as:

$$\mathrm{Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)}$$

• Why the correct option is right:
• Statement (B) is correct because there is an exchange of ions ($$\mathrm{Ba^{2+}}$$ and $$\mathrm{SO_4^{2-}}$$, and $$\mathrm{Na^+}$$ and $$\mathrm{Cl^-}$$) between the reactants.
• Statement (C) is correct because a white precipitate of barium sulphate ($$\mathrm{BaSO_4}$$) is formed.
• Statement (D) is correct because a precipitate is, by definition, an insoluble salt that separates from the solution.

Since (B), (C), and (D) are all correct, option (D) is the right choice.

• Why the distractors are wrong:
• Statement (A) is incorrect because the reaction involves the exchange of ions in solution, not neutral atoms. Thus, any option containing (A) or omitting (C) and (D) is incomplete or incorrect.