Diffusion is of

Options

A. One substance depends on another substance
B. The only means of gaseous movement in plants
C. An energy dependent process
D. Solid is more common than gases or liquids

Answer

### Step-by-Step Solution:

1. **Understanding Diffusion**:
- Diffusion is defined as the movement of substances from one region to another. Specifically, it refers to the movement of particles from an area of high concentration to an area of low concentration.

2. **Direction of Movement**:
- The key characteristic of diffusion is that it occurs from a region of higher concentration to a region of lower concentration. This means that particles will naturally spread out to fill the available space.

3. **Medium of Diffusion**:
- Diffusion is most prominent in gases and liquids. In gases, the particles are far apart and move freely, allowing for rapid diffusion. In liquids, diffusion occurs but is generally slower due to closer particle proximity.

4. **Osmosis vs. Diffusion**:
- It is important to distinguish diffusion from osmosis, which is a specific type of diffusion that involves the movement of water across a semipermeable membrane. Osmosis is more relevant in the context of liquids.

5. **Evaluating Options**:
- **Option 1**: "Diffusion is of one substance depends on another substance."
- This is incorrect because diffusion depends on concentration gradients, not on the substances involved.
- **Option 2**: "Only means of gaseous movement in plants."
- This is correct as diffusion is the primary method for gas exchange in plants, occurring through stomata.
- **Option 3**: "An energy-dependent process."
- This is incorrect because diffusion occurs without the need for energy; it is a passive process driven by concentration gradients.
- **Option 4**: "Solid is more common than gases or liquids."
- This is incorrect as diffusion is more common in gases and liquids, not solids.

6. **Conclusion**:
- Based on the evaluation, the only correct statement regarding diffusion is **Option 2**, which states that diffusion is the only means of gaseous movement in plants.