That really depends on whether you boil all the five eggs together or you boil them one by one. In first case it would take only five minutes to boil all the five eggs. But in the second case it may take up to 25 minutes to get it done.
The answer to the question is C which is 5 minutes. The reason being that if the eggs are boiled together, it will still take the same amount of time it took to boil one egg to boil 5 eggs.