Answer:
When the temperature of substance is lower then the distance between molecule of goes to decreases.When the distance between molecule decreases then the substance become denser.So the density of substance increases.
On the other hand when the temperature of substance increases then the distance between molecule of goes to increases.When the distance between molecule increases then the substance become less denser.So the density of substance decreases.
That is why hot water is less denser as compare to cold water.In cold water the distance between is less as compare to hot water molecule.