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.

Physical testing of paper is essential to evaluate its quality and suitability for specific applications. The standard physical tests employed in the paper manufacturing industry include:

I. Mechanical and strength properties: These tests measure tensile strength, tearing resistance, bursting strength, folding endurance, and stiffness.

II. Surface properties: These tests evaluate smoothness, friction, and abrasion resistance, which are important for printing and handling.

III. Optical properties: These tests determine brightness, opacity, gloss, and color, which affect the visual appearance of the paper.

IV. Permeability to fluids: These tests assess air permeability, water absorbency, and oil penetration, which are crucial for packaging and printing applications.

Since all the listed properties are evaluated through physical tests during paper manufacture, I, II, III, and IV are correct.

Answer: I, II, III and IV