There are some deposits of nitrated and phosphates in the earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under laboratory conditions but microbes do it easily. Ammonia forms a large number of complexes with transition metal ions. Hybridisation easily explains the ease of sigma donation capability of `NH_3` and `PH_3`. Phosphine is a flammable gas and is prepared from white phosphorous.
Which of the following statement is correct ?

Options

A. Phosphates have no biological significance in humans.
B. Between nitrates and phosphates, phosphates are less abundant in earth's crust.
C. Between nitrates and phosphates, nitrates are less adundant in earth's crust.
D. Oxidation of nitrates is possible in soil.

Explanation

To determine which statement is correct regarding nitrates and phosphates based on the provided information, we can analyze each statement step by step.

### Step 1: Analyze the first statement
The first statement claims that phosphates have no biological significance in humans.
- **Evaluation**: This is incorrect because phosphates are essential for the formation of bones and teeth, as well as for various biological processes such as energy transfer (ATP).

**Hint**: Remember the role of phosphates in biological systems, particularly in skeletal structures.

### Step 2: Analyze the second statement
The second statement asserts that phosphates are less abundant in the earth's crust compared to nitrates.
- **Evaluation**: This is also incorrect. The paragraph indicates that nitrates are more soluble in water, which leads to their leaching and reduced abundance in the earth's crust. Therefore, phosphates are generally more abundant than nitrates.

**Hint**: Consider the solubility of nitrates and how it affects their abundance in the earth's crust.

### Step 3: Analyze the third statement
The third statement states that nitrates are less abundant in the earth's crust.
- **Evaluation**: This statement is correct. The information provided indicates that nitrates are more soluble in water, leading to their reduced presence in the earth's crust due to leaching.

**Hint**: Focus on the relationship between solubility and abundance in geological deposits.

### Step 4: Analyze the fourth statement
The fourth statement claims that the oxidation of nitrates is possible in soil.
- **Evaluation**: This statement is incorrect. Nitrates have nitrogen in the +5 oxidation state, and nitrogen cannot be oxidized beyond this state. Instead, nitrates are typically reduced by microbes in the soil.

**Hint**: Recall the oxidation states of nitrogen and the chemical behavior of nitrates.

### Conclusion
After analyzing all statements, the only correct statement is that nitrates are less abundant in the earth's crust (Statement C).

### Final Answer
The correct statement is: **Nitrates are less abundant in the earth's crust.**