The correct option is C decrease
Water behaves differently unlike most other substances, in the sense that it becomes denser as it melts. So, it takes less volume for the same mass upto 4∘C, after which the density of water increases with increase in temperature. Because of this, ice actually contracts when it melts into water, i.e. its volume decreases even when the mass remains the same. In other words, a gram of ice has more volume than a gram of water at 0∘C.