Answer:
Ooo , this a tricky one. Alright , so basically it depends upon the temperature of water whether it be 50 or 150ml, so if it is supposed to reach room temp , (according to your question) it means that water is at a higher temperature than that of the room , so that heat flows from water to room and cools down till it reaches room temperature.
Both quantities will cool down.But the one which will cool down faster is the 150ml of water because 150ml has more mass and therefore has more specific heat capacity(conducts more heat) , it has a higher temperature than that of the 50ml of water, the one which has even higher temp will cool down faster , which is indeed the 150ml of water.