The collection of rare coins, many of which are centuries old, were acquired by the museum for an undisclosed sum.
✓ Correct Answer: Option B
The subject of the sentence is 'collection' (singular), not 'coins.' The verb must agree with the singular subject. Therefore, 'was acquired' is the correct verb form. Options A, C, and D incorrectly use the plural verb 'were' or have other grammatical errors.