Question

Match List-I with List-II

List-I	List-II
(A) Falling rate period	(I) Ratio of humidity with respect to humidity at saturation point
(B) Absolute humidity	(II) Critical moisture content
(C) Percent humidity	(III) Equilibrium moisture content
(D) Constant rate period	(IV) Ratio of kg of water vapour in kg of dry air

Choose the correct answer from the options given below:

• A. (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
• B. (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
• C. (A)-(I), (B)-(II), (C)-(IV), (D)-(III)
• D. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

Hint:

Work out the two humidity terms from their plain definitions first, then think about which drying period ends at critical moisture content and which one ends at equilibrium moisture content.

Answer 1

The Correct Option is D

Step 1: Absolute humidity is defined plainly as the mass of water vapour carried per unit mass of dry air, in other words kg of water vapour per kg of dry air. That is exactly (IV), so B-(IV).

Step 2: Percent humidity (percentage humidity) is defined as the ratio of the air's actual humidity ratio to the humidity ratio the same air would have if it were saturated at that same dry bulb temperature, expressed as a percentage. That is exactly the wording of (I), so C-(I).

Step 3: During drying, the constant rate period lasts only as long as free moisture keeps the grain's surface wet, so the drying rate stays flat. This period ends the instant the average moisture content drops to the critical moisture content, the point where surface moisture can no longer keep up with the evaporation demand. So the constant rate period is bounded by (II) Critical moisture content, giving D-(II).

Step 4: After that comes the falling rate period, where the drying rate keeps dropping as moisture has to migrate from inside the grain out to the surface. This period keeps going, slower and slower, until the moisture content nears the equilibrium moisture content, the lowest value the grain can reach under that air condition, where drying essentially stops. So the falling rate period pairs with (III) Equilibrium moisture content, giving A-(III).

Step 5: Putting these together: (A)-(III), (B)-(IV), (C)-(I), (D)-(II), which is option 4.