What is the general tone of a "soporific" substance?

The tone of a "soporific" substance relates to its primary effect on the body and mind, which is to induce sleep or a state of calmness. The word "soporific" originates from the Latin term "sopor," meaning deep sleep. Such substances are often used to alleviate insomnia or other conditions that prevent restful sleep. Therefore, a soporific substance is characterized by a calming and sleep-inducing quality, making "calming and sleep-inducing" the correct choice.

The other choices contrast with the defining feature of soporifics. Substances that are exciting and engaging or stimulating and energizing serve to increase alertness and activity levels, opposing the intended effects of soporifics. 'Neutral and indifferent' does not capture the specific and purposeful action of inducing sleep, as it lacks any connotation of effect, good or bad, and fails to address the characteristic impact that a soporific has. Thus, the correct answer encapsulates the essence of a soporific's function accurately.