Two needles are floating on the surface of water. A hot needle when touches water surface between the needles, then they move

Surface film of a liquid has a tendency to shrink and this tendency decreases with decrease in surface tension. When the hot needle is gently placed in the region 2, temperature of water in that region increases, increase in temperature reduces the surface tension, As a result, due to the shrinkage of surface film of water in regions 1 and 3, the cold needles C1 and C2 move away from each other.