Conc. `H_2 SO_4` is not a

Options

A. Dehydration agent
B. Hygroscopic
C. Oxidising agent
D. Efflorescent

Answer

To solve the question "Concentrated H2SO4 is not a...", we need to analyze the properties of concentrated sulfuric acid (H2SO4) and determine which of the given options does not apply to it.

### Step-by-Step Solution:

1. **Understand the Properties of Concentrated H2SO4:**
- Concentrated H2SO4 is known for several key properties: it acts as a dehydrating agent, is hygroscopic, and can function as an oxidizing agent.

2. **Evaluate Each Option:**
- **Dehydrating Agent:**
- A dehydrating agent is a substance that removes water from other compounds. Concentrated H2SO4 has a strong affinity for water and can remove water from compounds, making it a dehydrating agent.
- **Hygroscopic:**
- Hygroscopic substances are those that absorb moisture from the atmosphere. Concentrated H2SO4 readily absorbs water vapor from the air, confirming that it is hygroscopic.
- **Oxidizing Agent:**
- An oxidizing agent is a substance that can accept electrons and thereby oxidize another substance. In concentrated H2SO4, sulfur is in the +6 oxidation state, allowing it to act as an oxidizing agent.
- **Efflorescent:**
- Efflorescent substances are those that lose water of crystallization to the atmosphere. Since concentrated H2SO4 has a high affinity for water and absorbs moisture rather than losing it, it is not efflorescent.

3. **Conclusion:**
- Based on the analysis, concentrated H2SO4 is not an efflorescent substance. Therefore, the correct answer to the question is that concentrated H2SO4 is not an efflorescent agent.

### Final Answer:
Concentrated H2SO4 is not an efflorescent substance.