Heat can be transferred through conduction, convection, and radiation. what is necessary in order for heat to be transferred by conduction?

The objects must be in direct contact with one another.

Explanation: "Heat is transferred by conduction when objects are in direct contact with one another.

Heat transfer through space is radiation, and heat transfer through currents in liquids or gases is convection"

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.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.