A double displacement reaction is one in which the positive and negative ion in one reactant switch places with the positive and negative ions of the second reactant forming two new products.
In general if we have two reactants AB and CD, the double displacement reaction can form the following products:
A⁺B⁻ + C⁺D⁻ → C⁺B⁻ + A⁺D⁻
In the given example:
K₂SO₄ + Pb(NO₃)₂ → PbSO₄ + 2KNO₃
Ans: B)
One of the products would be PbSO₄