Assertion (A): The needle of a magnetic compass kept in strong external magnetic field, always aligns itself in north-south direction on the earth.

Reason (R): Behaviour of the needle of a compass is same as that of a freely suspended bar magnet.

As per the NCERT chapter, "A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole." This makes Reason (R) correct — the compass needle behaves exactly like a freely suspended bar magnet, since it essentially is a small bar magnet.

However, Assertion (A) is false. A compass needle normally aligns itself along the north-south direction only because, in the absence of any nearby magnet or current-carrying conductor, the only magnetic field acting on it is the earth's own magnetic field, and a freely suspended magnet always aligns along the direction of the net magnetic field acting on it. The chapter's activities repeatedly demonstrate this: "Place the compass near the north pole of the magnet. How does it behave? The south pole of the needle points towards the north pole of the magnet..." and "Observe the direction of deflection of the north pole of the needle. If the current flows from north to south... the north pole of the compass needle would move towards the east." These activities show that when a strong external magnetic field (from a bar magnet or a current-carrying wire) is brought near the compass, the needle deflects away from north-south and aligns instead along the direction of the resultant (stronger) external field — it does not stay fixed in the north-south direction. In fact, the chapter notes that increasing the current (i.e., strengthening the external field) increases the deflection: "if the current is increased, the deflection also increases," confirming that a strong external field overrides the earth's field and pulls the needle away from north-south.

Why the other options are wrong:

• Option A is wrong because although R is true, A itself is false, so R cannot be a correct explanation of a false statement.
• Option B is wrong for the same reason — A is not true, so both cannot be true.
• Option C is wrong because it has A and R reversed relative to the actual case; here R (not A) is the true statement, while A is false.

Thus only option D correctly captures that A is false while R is true.