Which of the following is/are the physical test(s) employed for the manufacture of paper?

I. Mechanical and strength properties

II. Surface properties

III. Optical properties

IV. Permeability to fluids

Select the correct answer using the code given below.

In the paper manufacturing industry, several physical tests are conducted to ensure quality and suitability for specific applications. Mechanical and strength properties (Statement I) include parameters like tensile strength, bursting strength, and tearing resistance. Surface properties (Statement II) measure characteristics like smoothness, roughness, and surface strength (wax pick), which are vital for printing. Optical properties (Statement III) involve testing for brightness, opacity, and color to ensure visual quality. Permeability to fluids (Statement IV) includes air permeability and liquid absorption tests (such as the Cobb test), which determine how the paper reacts to moisture and ink. Since all these categories are standard physical testing protocols used globally (e.g., by TAPPI and ISO standards) during and after the manufacturing process, all four statements are correct.