Alkalis are :

Options

A. acids, which are soluble in water
B. acids, which are insoluble in water
C. bases, which are insoluble in water
D. bases, which are soluble in water

Explanation

**Step-by-Step Solution:**

1. **Definition of Alkalis:**
Alkalis are a subset of bases that are soluble in water. They typically release hydroxide ions (OH⁻) when dissolved in water.

2. **Examples of Alkalis:**
Common alkalis include sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH). These compounds are formed when alkali metals react with water.

3. **Properties of Alkalis:**
- Alkalis are basic in nature, meaning they can neutralize acids.
- They increase the concentration of hydroxide ions (OH⁻) in an aqueous solution.

4. **Chemical Reaction with Water:**
When alkalis dissolve in water, they dissociate into their respective ions. For example:
- Sodium hydroxide (NaOH) dissociates into Na⁺ and OH⁻ ions.
- This dissociation increases the concentration of OH⁻ ions in the solution, confirming their basic nature.

5. **Conclusion:**
Therefore, alkalis are defined as bases that are soluble in water and produce hydroxide ions when dissolved.

**Final Answer:**
Alkalis are bases that are soluble in water.

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