Explanation:

External fragmentation occurs when free memory is split into small non-contiguous blocks (holes), even though the total free space is enough to satisfy a request.

In other words, the memory request cannot be allocated because the available free memory is scattered across different locations rather than being one large contiguous block.

Example: If total free memory = 100 MB, but it is divided into small pieces (20 MB, 30 MB, 50 MB) scattered in memory, then a process requesting 60 MB cannot be allocated, even though total free memory > 60 MB.

Hence, the correct answer is:

(A) When enough total memory space exists to satisfy a request, but it is not contiguous — storage is fragmented into a large number of small holes.

\[ \therefore \;\; \text{Correct answer is (A).} \]