Concept:
Jam preparation requires clean, sound and properly prepared fruits.
Step 1: Check Assertion.
Fruits must be washed thoroughly before jam preparation to remove dust, dirt, pesticide residues and microorganisms.
\[
A \text{ is correct}
\]
Step 2: Check Reason.
Leaves, stalks and damaged portions should be removed before processing. They should not remain attached during jam preparation.
\[
R \text{ is incorrect}
\]
Step 3: Final conclusion.
Assertion is correct, but Reason is incorrect.
\[
\therefore \text{Correct Answer is (C)}
\]