(C) Assertion (A) is true, but Reason (R) is false.
Assertion is correct. Reason is false because 290 K is a high melting point (not low), which causes pure ethanoic acid to freeze in winter, giving it the name glacial acetic acid.
The textbook states the melting point of pure ethanoic acid is 290 K and that it often freezes during winter, which is why it is called glacial acetic acid — so the Assertion is true. However, the Reason calls 290 K a "low melting point," which is incorrect; 290 K (≈17°C) is relatively high for an organic liquid, and it is this comparatively high melting point that causes freezing in cold climates. Since the Reason contains a factual error, option (C) is correct.