Which type of property can be observed only by changing a substance into a different substance?

chemical property.

Explanation:

The chemical properties are the capacity or incapacity of a substance to transform into one or more different substance either by reacting with one or more different substances or by decomposition.

Such properties can only be observed when such change (reaction) takes place and the substance, therefore, is transformed into one or more different substances.

On the other hand, the physicial properties can be observed or measured without changing the composition of the sample.

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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