There are two buckets A and B. There are two buckets A and B. Initially A has 2 litres of water and B is empty. At every hour 1 litre of water is transferred from A to B followed by returning litre back to A from B half an hour later. The earliest A will get empty is in: A) $1.5h$ B) $4h$ C) $3h$ D) $2h$

There are initially 2 liters. At the one hour mark we remove a liter to get 1 liter. At 1.5 hours we add half a liter to get 1.5 liters. At 2 hour mark we remove a liter to get 0.5 liters. At 2.5 hour mark we add half a liter to get 1 liter. At 3 hour mark we remove a liter to get 0 liters, and we are finished. Thus, the answer is $3$ hours. (this assumes we make the first transfer at the one hour mark instead of the zero hour mark, and that a half liter is added only added every other half hour (I. E. at noninteger hour points)