At what temperature does the solid start melting? –20°c 0°c 20°c 80°c

Therefore, At 0 °C solid starts melting.

Explanation:

The melting point of a substance is the temperature at which it changes state from solid to liquid.

Different substance have different melting point.

The melting point of ice at 1 atmosphere of pressure is very  to 0 °C  this is also known as the ice point.

answer: the rate of diffusion increases with increase in temperature.

increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material.

generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.