Acids are chemical substances that can donate protons (H+) or accept a pair of electrons in a chemical reaction. They typically have a sour taste and can react with bases to form salts and water.

Among the options given, the correct answer is A, B, and D, which are metaphosphoric acid, pyrosulfuric acid, and pyrophosphoric acid, respectively. Let's discuss each of these acids in detail:

1. Metaphosphoric acid (HPO3):
- Metaphosphoric acid is a strong acid that is commonly used as a food preservative and in laboratory applications.
- It is a clear, colorless liquid that can react with bases to form phosphates.
- The chemical formula of metaphosphoric acid is HPO3, and it is composed of phosphorus, oxygen, and hydrogen atoms.

2. Pyrosulfuric acid (H2S2O7):
- Pyrosulfuric acid is a strong acid with the chemical formula H2S2O7.
- It is a highly corrosive, oily liquid that is formed by the reaction of sulfuric acid with sulfur trioxide.
- Pyrosulfuric acid is used in various industrial applications, including as a dehydrating agent and in the production of dyes and pharmaceuticals.

3. Metasulfuric acid (H2SO5):
- Metasulfuric acid is a powerful oxidizing agent that is formed when sulfur trioxide reacts with water.
- It has the chemical formula H2SO5 and is a white crystalline solid.
- Metasulfuric acid is used in organic synthesis and as a bleaching agent.

4. Pyrophosphoric acid (H4P2O7):
- Pyrophosphoric acid is a weak acid that is formed by the dehydration of phosphoric acid.
- It has the chemical formula H4P2O7 and is a white crystalline solid.
- Pyrophosphoric acid is commonly used as a catalyst in various chemical reactions and as a pH regulator in food products.

In summary, metaphosphoric acid, pyrosulfuric acid, and pyrophosphoric acid are all examples of acids. These acids have different chemical formulas and properties but share the characteristic of being able to donate protons in chemical reactions.