Charles's law describes the relationship of the volume and temperature of
gas at a constant mass and pressure. according to this law, what would
happen to the volume of the gas if its temperature decreased from 400 k to
300 k?

the volume will decrease

Explanation:

an increase in temperature will lead to an increase in effective collision which also result in an increase in volume, when the temperature decreases, the volume will decrease

the transfer of heat by electromagnetic radiation is called thermal radiation . it is usually carried out by electromagnetic waves in an energy range just below the visible spectrum, which is the infrared range.

so the answer would be radiation.

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