ANS:C - sub-sonic

f the Mach number for a fluid flow is less than 1, the flow is considered subsonic. The Mach number (Ma) is a dimensionless quantity that represents the ratio of the speed of an object (or fluid flow) to the speed of sound in the medium through which it is traveling. Mathematically, it is defined as: Ma=av​ Where:

• v is the velocity of the object or fluid flow,
• a is the speed of sound in the medium.

When the Mach number is less than 1, it indicates that the speed of the object or fluid flow is less than the speed of sound in the medium. In such cases, the flow is classified as subsonic. If the Mach number is exactly 1, the flow is considered sonic, meaning that the object or fluid flow is traveling at the speed of sound. If the Mach number is greater than 1, the flow is classified as supersonic, indicating that the object or fluid flow is traveling faster than the speed of sound. Therefore, if the Mach number for a fluid flow is less than 1, the flow is subsonic.