Which of the following statement is correct?

Options

A. Calcium inhibits the translocation of manganese
B. Calcium deficiency is first reported in old leaf
C. In grasses, Si provides the mechanical strength
D. Nitrogenase catalyse the conversion of `NH_(3)` to `N_(2)`

Answer

To determine which statement is correct, we will analyze each option provided in the question:

1. **Option 1: Calcium inhibits the translocation of manganese.**
- This statement is incorrect. Manganese is a micronutrient, and when present in excess, it can lead to manganese toxicity. In this condition, manganese inhibits the translocation of calcium, not the other way around.

2. **Option 2: Calcium deficiency is first reported in old leaf.**
- This statement is also incorrect. Calcium is an immobile element in plants, meaning that its deficiency symptoms appear first in the young leaves, not the old leaves. In contrast, deficiencies of mobile elements like nitrogen, phosphorus, potassium, and sulfur are first observed in older leaves.

3. **Option 3: In grass, silica provides mechanical strength.**
- This statement is correct. Silica is known to contribute to the mechanical strength of grass, helping it to withstand environmental stresses.

4. **Option 4: Nitrogenous catalyzes the conversion of ammonia to nitrogen.**
- This statement is incorrect. Nitrogenous compounds are involved in the conversion of nitrogen gas (N2) to ammonia (NH3) through the process of nitrogen fixation, not the other way around.

After analyzing all options, we conclude that the correct answer is **Option 3: In grass, silica provides mechanical strength.**

### Step-by-Step Solution:
1. Analyze Option 1: Calcium inhibits manganese translocation. (Incorrect)
2. Analyze Option 2: Calcium deficiency appears in old leaves. (Incorrect)
3. Analyze Option 3: Silica provides mechanical strength in grass. (Correct)
4. Analyze Option 4: Nitrogenous converts ammonia to nitrogen. (Incorrect)
5. Conclude that the correct statement is Option 3.