Question

The processes of removal of particles in a rapid sand filter with their description is given in the table.

Process	Description
(i) Straining	P: Removes only particles in the water large enough to get caught in the pores of the filter
(ii) Sedimentation	Q: Larger and heavier particles do not follow the fluid streamline around the sand grain and settle on the grain
(iii) Interception	R: Particles that do follow the streamline, but are too large and are caught because they brush up against the sand grains
(iv) Diffusion	S: Very small particles are experiencing Brownian motion and may collide with the sand grains by chance

Select the correct match.

• A. i- S; ii-P; iii-Q; iv-R
• B. i-Q; ii-R; iii-S; iv-P
• C. i-R; ii- S; iii- P; iv-Q
• D. i-P; ii-Q; iii-R; iv-S

Answer 1

The Correct Option is D

Step 1: Analyze each process and its description. 
Straining (i): Removes only particles large enough to be trapped in the filter pores. Matches with \( P \). 
Sedimentation (ii): Larger and heavier particles settle due to gravity, not following the fluid streamline. Matches with \( Q \). 
Interception (iii): Particles follow the streamline but are too large and brush against sand grains, getting caught. Matches with \( R \). 
Diffusion (iv): Very small particles experience Brownian motion and collide with sand grains randomly. Matches with \( S \). 

Step 2: Select the correct match. From the analysis: \[ i: P, \quad ii: Q, \quad iii: R, \quad iv: S \]