Which of the following is used in pyro-techniques 

Options

A. `NH_(3)`
B. `HNO_(3)`
C. `PH_(3)`
D. `H_(3)PO_(4)`

Answer

To determine which compound is used in pyrotechnics, we need to analyze the given options based on their properties and applications in creating fireworks and similar effects.

### Step-by-Step Solution:

1. **Understanding Pyrotechnics**:
- Pyrotechnics is the science and craft of creating fireworks and other materials that produce effects such as heat, light, sound, gas, or smoke.

2. **Analyzing the Options**:
- We are provided with four compounds:
- Ammonia (NH3)
- Nitric Acid (HNO3)
- Phosphine (PH3)
- Phosphoric Acid (H3PO4)

3. **Evaluating Each Compound**:
- **Ammonia (NH3)**:
- Ammonia is hygroscopic, meaning it absorbs moisture from the air. This property makes it unsuitable for use in pyrotechnics as it does not produce the desired effects.
- **Nitric Acid (HNO3)**:
- While nitric acid is a strong oxidizer, it does not produce the necessary effects (heat, light, sound) required for pyrotechnics. Thus, it is not used in this field.
- **Phosphine (PH3)**:
- Phosphine is a flammable gas but does not fulfill the requirements of producing heat, light, sound, or smoke in a controlled manner for pyrotechnic applications.
- **Phosphoric Acid (H3PO4)**:
- Phosphoric acid, particularly in its red phosphorus form, is widely used in pyrotechnics. It meets all the necessary criteria for producing heat, light, sound, gas, and smoke.

4. **Conclusion**:
- Based on the analysis, the compound that is used in pyrotechnics is **Phosphoric Acid (H3PO4)**.

### Final Answer:
**H3PO4 (Phosphoric Acid)** is used in pyrotechnics.

---