Which description correctly contrasts instantaneous and quasi-steady releases?

• A. Instantaneous releases in negligible time (a puff); quasi-steady maintains roughly constant mass flow rate over a finite duration.
• B. Instantaneous releases at a constant rate; quasi-steady is a short impulse.
• C. Instantaneous is a continuous release; quasi-steady is an instantaneous event.
• D. Instantaneous release lasts longer than quasi-steady release.

Answer: (A)

Instantaneous releases are extremely brief events that deliver mass in a negligible amount of time, effectively an impulse or puff. Quasi-steady releases, on the other hand, extend over a finite duration and have a mass flow rate that remains roughly constant during that time.

This means the instantaneous release is a sharp, short surge, while a quasi-steady release is a sustained, near-constant flow. The other descriptions mix up duration and rate: an instantaneous event isn’t a constant-rate process, and a quasi-steady release isn’t just a brief impulse. Consequently, the described contrast—a puff-like, negligible duration versus a finite-duration, nearly constant flow—best captures the difference.