The Operating System of a computer may periodically collect all the free…

Free memory in a system often ends up scattered as many small unused holes between allocated blocks — external fragmentation — even when the total free space is large enough for a request, because no single hole may be big enough to satisfy it. One class of memory-management technique addresses this by relocating currently-used (live) memory together and merging every freed hole into one large contiguous block.

For this item, that periodic “gather every free hole into one contiguous block” operation is what a compacting garbage collector performs: it identifies the memory still referenced (in use), moves that live data together toward one end, and leaves the remaining space as a single free region. Contrasting against the offered choices by what each actually means:

• Garbage collection — reclaims unused memory and compacts the surviving data, merging the freed space into one contiguous block, which matches the stem.

• Concatenation — joins data sequences together; it says nothing about consolidating free memory regions.

• Collision — a hash-table or networking conflict between two items, unrelated to memory consolidation.

• Dynamic Memory Allocation — hands memory out to a process on request, the opposite direction of gathering free memory back.

Cross-checking against the official ISRO CS 2018 answer key for this exact previous-year question confirms Garbage collection as the keyed choice, consistent with the mark-compact garbage-collection model above.