I think is letter C, good luck!
A. When the substance is in its gaseous state.
<u>Explanation:</u>
When a substance is expanding against its constant volume and pressure, its temperature increases except when the substance is in gaseous state and not in liquid or solid state. So the internal energy increase in the system not only increases and maintaining the volume and pressure of the system remains constant in its gaseous phase. In the first law of Thermodynamics, it is used specifically that to especially in the case of gaseous system.
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"S<span>cientists believe that solids are mostly open space" is the statement among the statements given in the question that is true. The correct option among all the options that are given in the question is the second option or option "B". I hope that this answer has actually come to your help.</span>
