Answer :
(A) The balanced molecular equation will be:

(B) The balanced molecular equation will be:

(C) The balanced molecular equation will be:

(D) The balanced molecular equation will be:

Explanation :
Molecular equation : It is defined as a balanced chemical equation where the ionic compounds are expressed in the form of molecules rather than component of ions.
Precipitation reaction : It is defined as the reaction in which an insoluble salt formed when two aqueous solutions are combined.
The insoluble salt that settle down in the solution is known an precipitate.
Part A : potassium carbonate and lead(II) nitrate
The balanced molecular equation will be:

In this reaction, lead carbonate is an insoluble salt and potassium nitrate is a soluble solution.
Part B : lithium sulfate and lead(II) acetate
The balanced molecular equation will be:

In this reaction, lead sulfate is an insoluble salt and lithium acetate is a soluble solution.
Part C : copper(II) nitrate and sodium sulfide
The balanced molecular equation will be:

In this reaction, Cuprous sulfide is an insoluble salt and sodium nitrate is a soluble solution.
Part D : strontium nitrate and potassium iodide
The balanced molecular equation will be:

In this reaction, strontium iodide and potassium nitrate are soluble solution.
