The fragmentation which cannot be fully eliminated is –

Concept: Fragmentation is wasted memory produced by a scheme's own allocation mechanics. Internal fragmentation is unused space left inside an already-allocated fixed-size unit (e.g., a page or a fixed partition), because that unit rarely matches a process's exact requirement. External fragmentation is unused space that appears between allocated blocks, as variable-size allocations and deallocations scatter free memory into small, non-contiguous holes over time.

Application: Trace what happens under each scheme:

1. Fixed-size allocation (paging/frames, fixed partitions) grants a process whole units; when its actual requirement is not an exact multiple of the unit size, the leftover space inside the last unit is internal fragmentation.

2. That leftover space stays locked inside the allocated unit and cannot be reassigned to another process, nor reduced to zero, without shrinking the unit size itself (which only trades it for higher management overhead) - so internal fragmentation persists as long as fixed-size allocation is used.

3. Variable-size allocation (dynamic partitioning, segmentation) instead lets processes take exactly the size they need; but as processes arrive and leave, the freed spaces get scattered into small, non-contiguous holes between allocated blocks - this is external fragmentation.

4. External fragmentation has a direct operational cure: compaction relocates every currently-allocated block together so the scattered holes merge into one contiguous block, removing external fragmentation completely, in principle.

5. Because external fragmentation has a technique that removes it entirely while internal fragmentation has no such fix short of abandoning fixed-size allocation altogether, the type that cannot be fully eliminated is internal fragmentation.

Cross-check:

• External fragmentation is not the answer, because compaction is a standard, well-documented technique that consolidates its scattered free memory into a single contiguous block.

• Both types together is not accurate either, since external fragmentation does have a full removal technique - treating the two as equally unremovable overstates that case.

• None of the listed options is also not right, since internal fragmentation does correctly name a fragmentation type that is structurally impossible to reduce to zero without changing the allocation scheme itself.

Note: everyday explanations sometimes stress how costly compaction is to run in practice and describe external fragmentation as the one that 'cannot be removed' - but strictly, compaction is a genuine complete-removal technique for external fragmentation, while internal fragmentation has no equivalent fix, which is why internal fragmentation is the standard keyed answer here.