explosive symbols are used to label materials that release great amounts of energy in all these forms…

Brief Explanations:

Explosive materials release energy as heat, light, sound and expanding pressure. There is no exception among these options in typical explosive - related energy releases. But if we assume a mis - understanding in the question setup, usually all these forms are associated with explosive energy release. However, if we have to pick one, there is no common situation where an explosive doesn't release one of these while releasing the others. But if we consider some very rare or non - typical scenarios, sound might be the least distinct in some low - intensity explosions or in cases where the medium doesn't carry sound well.

Answer:

C. Sound