Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The Reynolds number is used to characterize the type of fluid flow.
Reason (R): It represents the ratio of inertial forces to viscous forces.
Choose the correct answer from the options below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Low $Re$ → Laminar, High $Re$ → Turbulent.

Answer 1

The Correct Option is A

Concept: Reynolds number ($Re$) is a dimensionless quantity used in fluid mechanics to predict flow regimes such as laminar or turbulent flow.

Step 1: Definition of Reynolds number.
\[ Re = \frac{\rho v D}{\mu} \] where:
• $\rho$ = density
• $v$ = velocity
• $D$ = characteristic length
• $\mu$ = viscosity

Step 2: Physical interpretation.
Reynolds number represents:
• Ratio of inertial forces to viscous forces

Step 3: Evaluating Assertion (A).
It is used to classify flow as:
• Laminar
• Transitional
• Turbulent Thus, Assertion (A) is correct.

Step 4: Evaluating Reason (R).
Reason correctly explains the physical meaning of Reynolds number.

Step 5: Linking both statements.
Because flow regime depends on the balance of inertial and viscous forces, the ratio (Reynolds number) determines the type of flow. Final Conclusion:
Both statements are correct and Reason explains Assertion. Hence, option (1) is correct.