Find the number of metals from the given metals which can be commercially purified by zone refining methods :
`Si, Ge, Ga, Al, Ti, Zr`.

Explanation

To determine the number of metals from the given list that can be commercially purified by the zone refining method, we need to analyze each metal based on its properties and the suitability of the zone refining technique.

### Step-by-Step Solution:

1. **Understanding Zone Refining**:
- Zone refining is a purification technique based on fractional crystallization. It works on the principle that impurities tend to remain in the molten phase while the pure metal crystallizes out.
- This method is particularly effective for materials where the solubility of impurities in the solid state is significantly lower than in the liquid state.

2. **Analyzing Each Metal**:
- **Silicon (Si)**: Silicon is a semimetal and is commonly purified using zone refining due to its application in the electronics industry.
- **Germanium (Ge)**: Germanium is also a semimetal and can be purified using zone refining. It is used in semiconductor applications.
- **Gallium (Ga)**: Gallium is a metal that can be purified by zone refining, especially for high-purity applications.
- **Aluminum (Al)**: Aluminum is typically purified using other methods such as electrolysis and is not suitable for zone refining.
- **Titanium (Ti)**: Titanium is usually purified through methods like the Kroll process and is not commonly purified by zone refining.
- **Zirconium (Zr)**: Zirconium is also not typically purified by zone refining; it is usually purified through other metallurgical processes.

3. **Counting the Suitable Metals**:
- From the analysis, the metals that can be commercially purified by zone refining are:
- Silicon (Si)
- Germanium (Ge)
- Gallium (Ga)
- Therefore, there are **three metals** from the given list that can be purified by zone refining.

### Final Answer:
The number of metals from the given list that can be commercially purified by zone refining methods is **3**.