Which of the statement are in accordance with the observation of geographer Alexander von Humboldt ?
I. Within a region species, richness increases with increasing explored area but within a limit.
II. The relation between species richness and area is a rectangular hyperbola.
III. The richness of species decreases with the increasing explored area.
IV. There is no relation between the explored area and species richness .

Options

A. I and II only
B. I , III and IV
C. II and IV
D. II and III

Answer

To solve the question regarding the observations of geographer Alexander von Humboldt, we will analyze each statement provided and determine which ones align with his findings.

### Step-by-Step Solution:

1. **Understanding Humboldt's Observation**:
- Alexander von Humboldt observed that species richness increases with the area explored, but only up to a certain limit. This means that as you explore a larger area, you will find more species, but after reaching a certain point, the increase in species richness levels off.

2. **Analyzing Each Statement**:
- **Statement I**: "Within a region species richness increases with increasing explored area but within a limit."
- This statement is **true** as it directly reflects Humboldt's observation.

- **Statement II**: "The relation between species richness and area is a rectangular hyperbola."
- This statement is also **true**. Humboldt's findings suggest that the relationship can be represented in this manner.

- **Statement III**: "The richness of species decreases with the increasing explored area."
- This statement is **false**. Humboldt's observations indicate that species richness increases with the explored area, not decreases.

- **Statement IV**: "There is no relation between the explored area and species richness."
- This statement is also **false**. Humboldt established a clear relationship between explored area and species richness, indicating that they are directly proportional.

3. **Conclusion**:
- The correct statements according to Humboldt's observations are **I and II**. Therefore, the answer to the question is that statements I and II are in accordance with the observations of Alexander von Humboldt.

### Final Answer:
The correct statements are **I and II**.