# Food Engineering Questions and Answers – Unit Operations – Diffusion and Mass Transfer-1

This set of Food Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Unit Operations – Diffusion and Mass Transfer-1”.

1. Shifting of a pair of ripened apples from the store house to the vegetable cart is called mass transfer.
a) True
b) False

Explanation: Shifting of a pair of ripened apples from the store house to the vegetable cart is only called material handling.

2. Statement 1: When alcohol is allowed to move from chamber A to chamber B when a barrier between them is removed, it is called multi phase diffusion.
Statement 2: When oxygen is made to diffuse into the water, it’s called continuous molecular diffusion.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Alcohol and water are miscible in each other. They aren’t different phases. Hence, it cannot be called multi phase diffusion. When oxygen is made to diffuse into water, it’s called continuous molecular diffusion.

3. Velocity gradient is the main driving force in mass transfer.
a) True
b) False

Explanation: Velocity gradient is the main driving force in momentum transfer.

4. Statement 1: A phase boundary exists between alcohol and oxygen.
Statement 2: Phase boundary varies with agitation. It is inversely proportional to the amount of agitation provided.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Both the statements pertaining to phase boundary are true.

5. A phase boundary between alcohol and water exists.
a) True
b) False

Explanation: Alcohol and water are miscible in each other. They aren’t different phases. Hence, no phase boundary exists.
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6. Statement 1: Diffusion is faster than convective mass transfer.
Statement 2: Mass transfer is proportional to the area of contact.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Convective mass transfer is faster than diffusion. Mass transfer is proportional to the area of contact.

7. Statement 1: Resistance is inversely proportional to the inter-facial area.
Statement 2: The inter-facial area of a body is the area of the dispersed phase in a unit volume of the vessel.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Resistance is inversely proportional to the inter-facial area. The inter-facial area of a body is the area of the dispersed phase in a unit volume of the vessel.

8. Ratio of equilibrium concentrations of solute A in liquid phase and gas phase i.e. CAL* and CAg* respectively is α. α is called _____
a) Diffusion coefficient
b) Distribution coefficient
c) Mass transfer coefficient
d) None of the mentioned

Explanation: CAL*/CAg* = α = Distribution coefficient.

9. Statement 1: Diffusion of gas component through the resistive film to the bulk of the liquid is the rate determining step.
Statement 2: Diffusion of gas component through the gas-liquid inter-phase is the rate determining step.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Diffusion of gas component through the resistive film to the bulk of the liquid is the rate determining step as the resistance during this is maximum.

10. In a packaging of dry grapes, the packaging material is made of polyethylene. The dry grapes have certain moisture content. Which of the following is true with respect to the diffusion of certain amount of moisture through the packing?
a) The moisture will not diffuse
b) The diffusion in this case is called permeability
c) None of the mentioned
d) Neither of the mentioned

Explanation: In packaging (especially polymers) terminology, the term diffusion is referred to as permeability.

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