Question

Two statements are given below: 
Statement I: Viscosity of liquid decreases with increase in temperature. 
Statement II: The units of viscosity coefficient are Pascal sec. The correct answer is:

• A. Both statement-I and statement-II are correct.
• B. Both statement-I and statement-II are not correct.
• C. Statement-I is correct but statement-II is not correct.
• D. Statement-I is not correct but statement-II is correct.

Hint:

Viscosity of liquids typically decreases with an increase in temperature. Additionally, the units of dynamic viscosity are Pascal seconds (Pa·s).

Answer 1

The Correct Option is A

To determine the correctness of the statements provided, let's analyze each statement one by one:

Statement I: Viscosity of liquid decreases with increase in temperature. 

As temperature increases, the kinetic energy of the molecules in a liquid increases, causing them to move more rapidly. This increased movement reduces the cohesive forces among the molecules, leading to a decrease in viscosity. Therefore, Statement I is correct.

Statement II: The units of viscosity coefficient are Pascal sec.

The viscosity coefficient is often measured in units of Pascal seconds (Pa·s). This is derived from the equation for dynamic viscosity, which is the ratio of shear stress (in Pascals) to shear rate (in sec⁻¹). Hence, Statement II is also correct.

Both statements are validated by the scientific principles of fluid dynamics and the units of physical measurements. Therefore, the correct answer is: Both statement-I and statement-II are correct.

Answer 2

Let's examine both statements: 
Statement I: Viscosity of liquid decreases with increase in temperature. 
This statement is correct. As temperature increases, the kinetic energy of molecules also increases, which reduces the intermolecular forces and allows molecules to move more freely. As a result, the viscosity of the liquid decreases.
Statement II: The units of viscosity coefficient are Pascal sec. 
This statement is also correct. The viscosity coefficient, also known as dynamic viscosity, is defined as the ratio of the shear stress to the shear rate. The units of viscosity are Pascal·second (Pa·s), which is equivalent to kg·m^-1·s^-1.
Since both statements are correct, the correct answer is:

\(\boxed{(A) \, \text{Both statement-I and statement-II are correct.}}\)