Assertion :- Mass or bulk flow is different from diffusion.
Reason:- In diffusion different substances move independently while in mass flow they move with same pace.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Assertion**: The assertion states that mass or bulk flow is different from diffusion. To analyze this, we need to define both processes.

2. **Defining Diffusion**: Diffusion is a passive transport process where molecules move from an area of higher concentration to an area of lower concentration. This movement occurs along a concentration gradient and does not require energy. The molecules move randomly and independently of each other.

3. **Defining Mass Flow**: Mass flow, also known as bulk flow, refers to the movement of substances in a fluid (like water or sap in plants) where all components move together in the same direction. This process is driven by pressure differences and is essential for the translocation of nutrients, such as sugars in plants, from sources (like leaves) to sinks (like roots).

4. **Analyzing the Reason**: The reason provided states that in diffusion, different substances move independently, while in mass flow, they move at the same pace. This is accurate because, in diffusion, each substance behaves according to its concentration gradient, whereas in mass flow, the substances are carried along together due to the bulk movement of the fluid.

5. **Conclusion**: Both the assertion and the reason are correct. The assertion correctly identifies that mass flow is different from diffusion, and the reason accurately explains how the two processes differ in terms of the movement of substances.

6. **Final Answer**: Therefore, the correct option is that both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.

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