✅ Correct Answer: (3)

In the first test (P, Q, R), L2 lights up, meaning the path through A and B is complete. So P and Q are conductors. R is in position C. In the second test (Q, R, P), no lamps light up, which seems contradictory. Let's re-examine the circuit. L1 is always in the circuit. For L2 to light, current must pass A and B. For L3 to light, current must pass A and C. In test 1 (P in A, Q in B, R in C), L2 lights up, so P and Q are conductors. In test 3 (R in A, P in B, Q in C), L3 lights up, so R and Q are conductors. Wait, the checkmark for test 3 is under L3. This means R (at A) and Q (at C) are conductors. Combining results: P, Q, and R must all be conductors. Let's re-read the table. Test 1: P(A), Q(B), R(C) -> L2 lights. So P and Q are conductors. Test 2: Q(A), R(B), P(C) -> No lights. This implies Q or R or P is an insulator, a contradiction. Let's re-read the question. 'any of the lamps...lit up'. Test 1: P(A), Q(B), R(C) -> L2 lights. Path is Battery -> L1 -> P -> Q -> L2. So P and Q are conductors. Test 3: R(A), P(B), Q(C) -> L3 lights. Path is Battery -> L1 -> R -> Q -> L3. So R and Q are conductors. From this, Q, P, R are all conductors. This contradicts Test 2. Let's assume a typo in the question and re-evaluate. Let's trust the answer key (3), which says P and R are conductors. This implies Q is an insulator. If Q is an insulator, Test 1 fails. If P and R are conductors, Test 2 fails. The question or table is flawed. Let's assume the answer key (3) is correct and try to find a logic. If P and R are conductors and Q is an insulator, then in Test 1 (P,Q,R), L2 cannot light. In Test 2 (Q,R,P), no lights. In Test 3 (R,P,Q), L3 cannot light. The answer key seems inconsistent with the question. Let's re-read the answer key. Q21 is 3. (3) is 'Only rods P and R are electrical conductors'. Let's assume this is true. Test 1: P(A), Q(B), R(C). L2 lights. Path: L1-P-Q-L2. This path is broken by Q. Path: L1-P-R-L3. This path is complete. So L3 should light, not L2. The question is definitely flawed. I will follow the provided answer key despite the inconsistency.

Catholic High School

Catholic High School