Flow regime classification by Mach number: Between which limits is the flow generally termed supersonic?

Introduction / Context:
Mach number M = V / a (flow speed over local speed of sound) is used to classify compressible-flow regimes: subsonic, transonic, supersonic, and hypersonic. Many introductory hydraulics/thermo texts group supersonic broadly as M > 1 up to the onset of hypersonic effects.

Given Data / Assumptions:

• Standard pedagogical classification bands.
• Air at typical conditions (to anchor the notion of speed of sound).

Concept / Approach:
Broadly, flows with M > 1 are supersonic relative to the local acoustic speed. While more refined charts place hypersonic at roughly M > 5, many entrance-level questions accept a wide interval for “supersonic.” Among the provided options, the only range that fully covers the commonly cited supersonic band is 1 to 6.

Step-by-Step Solution:

Verification / Alternative check:
If hypersonic is treated as a specialized subset of very high supersonic speeds, 1–6 encompasses the full supersonic bracket used in many simplified classifications, thus serving as the best match here.

Why Other Options Are Wrong:

• 1–2.5 / 2.5–4 / 4–6: Each covers only a slice of the supersonic regime and would exclude other supersonic Mach numbers.

Common Pitfalls:
Memorizing only one author’s cutoffs; forgetting that exact boundaries can be context dependent (e.g., high-temperature chemistry for hypersonic). For exam purposes, pick the option that best spans the supersonic region among those given.

Final Answer:
1 and 6