The composition of mica is

Options

A. `NaAlSiO_(4).3H_(2)O`
B. `K_(2)O.3Al_(2)O_(3).6SiO_(2).2H_(2)O`
C. `K_(2)OHAl(SiO_(4))_(3)`
D. `NaK.SiO_(4).10H_(2)O`

Explanation

To determine the composition of mica, we can analyze the provided options and the characteristics of mica as a mineral.

### Step-by-Step Solution:

1. **Understanding Mica**: Mica is a naturally occurring mineral that belongs to the silicate group. It is primarily composed of silicate minerals and contains various elements such as potassium (K), aluminum (Al), silicon (Si), oxygen (O), and water (H2O).

2. **Analyzing the Options**:
- **Option 1**: NaAlSiO4 · 3H2O
- **Option 2**: K2O · 3Al2O3 · 6SiO2 · 2H2O
- **Option 3**: K2AlSiO4 · 3
- **Option 4**: NaKSiO4 · 10H2O

3. **Identifying the Correct Formula**:
- Mica is known to have a general formula that includes potassium, aluminum, and silicate components. The most common type of mica is muscovite, which can be represented as KAl2(AlSi3O10)(OH)2·H2O.
- Among the options, we need to find a formula that reflects the presence of potassium, aluminum, silicon, and water.

4. **Evaluating Each Option**:
- **Option 1**: This formula contains sodium instead of potassium, which is not characteristic of mica.
- **Option 2**: This option includes K2O, Al2O3, and SiO2, which aligns with the composition of mica. The presence of water (H2O) also supports this.
- **Option 3**: This option lacks water and does not represent the complete composition of mica.
- **Option 4**: This option contains sodium and a high amount of water, which is not typical for mica.

5. **Conclusion**: After evaluating the options, **Option 2 (K2O · 3Al2O3 · 6SiO2 · 2H2O)** is the correct representation of the composition of mica.

### Final Answer:
The composition of mica is K2O · 3Al2O3 · 6SiO2 · 2H2O.