Two chemicals react in an endothermic reaction. What can be known about this reaction? The new substance will need more energy to form its chemical bonds than the old substance will release.
More energy will be released from the old substance than the new substance will need to form its chemical bonds.
A precipitate will form as a result of the reaction.
A gas will form as a result of the reaction.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

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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