Question

when a solid melts its temperature remain the same so where does the heat energy go

Answer 1

heat energy gets used up in changing the state because of the intermolecular force of attraction so that he gets used up in overcoming the force of attraction because if the force of attraction is very high then it is solid if very low then gas and if it is moderate then it is liquid depends upon the state but you have said that solid melts this means that it will melt to liquid obviously so the heat is overcome in changing the state so it the temperature remains the same

Answer 2

solid melts but it's temperature remain the same because the heat energy is used in changing the state of solid this process is called latent heat of evaporation