A flask of water rests on a scale. If you dip your finger into the water, withou

C

I would think it would decrease.  hmm  interesting.

assuming the finger to be perfectly frictionless so that no other force other than gravity and buoyant force acts on the finger and on the water level,
when you dip your finger in water, your finger displaces some of water. recall archimedes principle. So, there would be an upward buoyant force acting on your finger which is proportional to the amount of water displaced by you.
So, newton's third law states that to every action, there is equal and opposite reaction, so the water will face an equal amount of force(equal to buoyant force) on it by the finger causing the reading on the scale to increase.

answer is option c