Which among the following gas was called acid formerly?

Options

A. nitrogen
B. hydrogen
C. carbon dioxide
D. oxygen

Explanation

To solve the question "Which among the following gas was called acid formerly?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question is asking for a gas that was historically referred to as "acid".

2. **Identify the Options**: Although the options are not provided in the question, we need to focus on gases that are commonly known and have historical significance in chemistry.

3. **Recall Historical Context**: In historical chemistry, the term "acid former" was associated with certain gases. The most notable gas that fits this description is Oxygen.

4. **Analyze the Name of Oxygen**: The name "Oxygen" comes from Greek roots: "oxy" meaning "acid" and "genes" meaning "former". This indicates that Oxygen was believed to be a key component in the formation of acids.

5. **Conclusion**: Based on the historical context and the etymology of the name, we conclude that the gas that was formerly called "acid" is Oxygen.

6. **Select the Answer**: If we were to choose from options, we would select the option that states "Oxygen".

### Final Answer:
The gas that was formerly called acid is **Oxygen**.

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