Which of the following substance can be used directly as fertilizer?

Options

A. `(NH_(4))_(2)SO_(4)`
B. `Ca_(3)(PO_(4))_(2)`
C. `Ca(H_(2)PO_(4))_(2)`
D. `CaCN_(2)+C`

Explanation

To determine which of the given substances can be used directly as fertilizers, we need to analyze each option based on their solubility and nutrient content.

### Step-by-Step Solution:

1. **Understanding Fertilizers**:
- Fertilizers are substances added to soil to enhance its fertility by providing essential nutrients to plants. They can be chemical or natural.

2. **Analyzing Option A: Ammonium Sulfate (NH4)2SO4**:
- Ammonium sulfate is a soluble salt that provides nitrogen, an essential nutrient for plant growth.
- **Conclusion**: This can be used directly as a fertilizer.

3. **Analyzing Option B: Calcium Phosphate (Ca3(PO4)2)**:
- Calcium phosphate is a tertiary phosphate that is not soluble in water.
- Since it is not soluble, plants cannot absorb it effectively.
- **Conclusion**: This cannot be used directly as a fertilizer.

4. **Analyzing Option C: Calcium Dihydrogen Phosphate (Ca(H2PO4)2)**:
- Calcium dihydrogen phosphate is soluble in water and provides phosphorus, which is crucial for plant development.
- **Conclusion**: This can be used directly as a fertilizer.

5. **Analyzing Option D: Calcium Cyanamide (CaCN2)**:
- Calcium cyanamide is also soluble and provides nitrogen. It is used as a fertilizer.
- **Conclusion**: This can be used directly as a fertilizer.

6. **Final Conclusion**:
- Based on the analysis, the substances that can be used directly as fertilizers are:
- A: Ammonium Sulfate (NH4)2SO4
- C: Calcium Dihydrogen Phosphate (Ca(H2PO4)2)
- D: Calcium Cyanamide (CaCN2)

### Summary of Correct Answers:
- The substances that can be used directly as fertilizers are A, C, and D.