Explain the difference between internal and external fragmentation:

Given five variable sized memory partitions of $100$ kb$,500$ kb$,200$ kb$,300$ kb$,600$ kb $($in order$),$ how would each of the first fit, best fit, and worst fit algorithms place processes of $212$ kb$,417$ kb$,112$ kb$,$ and $426$ kb $($in order$)?$ Which algorithm makes most efficient use of memory?