All the gases are considered to have compressible flow and all the liquids are considered to have incompressible flow.

Compressibility refers to a fluid's ability to change its volume under pressure variations. Liquids are generally less compressible than gases, but all fluids exhibit compressibility to some extent.

Compressibility Based on Mach Number:

Incompressible Flow (Ma < 0.3): For Mach numbers less than 0.3, the density change in the flow is typically considered negligible for most engineering applications. This allows us to treat the fluid as incompressible, simplifying calculations. This is often the case with liquids at low velocities.
Compressible Flow (Ma >= 0.3): When the Mach number reaches 0.3 or higher, the density changes due to pressure variations become significant, even for liquids. In such cases, compressibility effects need to be taken into account for accurate analysis. This is especially true for high-speed flows or situations with large pressure variations.
So the above statement is incorrect.