The pair in which both the species have iron is:

Options

A. nitrgenase, cytochromes
B. carboxypeptidase, haemoglobin
C. haemocyanin. Nitrogenase
D. haemoglobin, cytochromes.

Explanation

To solve the question, we need to identify which pair of species contains iron in both of its components. Let's analyze each option step by step.

### Step 1: Analyze Option A
- **Nitrogenase**: This enzyme contains iron, specifically in the form of iron-sulfur clusters.
- **Cytochrome**: This protein also contains iron, which is crucial for its function in electron transfer.

**Conclusion for Option A**: Both species contain iron.

### Step 2: Analyze Option B
- **Carboxypeptidase**: This enzyme does not contain iron; it typically contains zinc as a cofactor.
- **Cytochrome**: As established, cytochrome contains iron.

**Conclusion for Option B**: Only one species contains iron (cytochrome), while carboxypeptidase does not.

### Step 3: Analyze Option C
- **Carboxypeptidase**: As previously mentioned, this enzyme does not contain iron.
- **Hemoglobin**: This protein contains iron, which is essential for oxygen transport.

**Conclusion for Option C**: Only one species contains iron (hemoglobin), while carboxypeptidase does not.

### Step 4: Analyze Option D
- **Hemoglobin**: Contains iron, which is crucial for its function in oxygen transport.
- **Cytochrome**: Contains iron, which is important for electron transfer.

**Conclusion for Option D**: Both species contain iron.

### Final Conclusion
The pair in which both species have iron is **Option D** (Hemoglobin and Cytochrome).

### Summary of the Solution
- **Option A**: Both have iron (Nitrogenase and Cytochrome).
- **Option B**: Only Cytochrome has iron.
- **Option C**: Only Hemoglobin has iron.
- **Option D**: Both have iron (Hemoglobin and Cytochrome).

Thus, the correct answer is **Option D**.