How can we decrease the melting point of ice?

The way is by adding salt. A substance dissolved in a liquid lowers the freezing point or melting point of that liquid. When salt is added to ice at room temperature, some of the ice melts and cools the salt to zero degrees Celsius. The salt solution thus produced cannot remain in equilibrium with ice at zero degrees. It is possible only when the ice at the freezing point of the solutions melts taking the necessary latent heat o fusion from the salt solution, whose temperature is consequently lowered. More salt thus dissolves, keeping the solution saturated and the process continues till the temperature of the solution is reduced to -21 degree Celsius. Only at this point, ice is in equilibrium with saturated salt solution. When 23 per cent of salt is added to ice, the freezing point is lowered to -21 degree Celsius.