Hydrogen can be obtained by its _____ from water, acids and alkalies by metals.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks how hydrogen can be obtained from water, acids, and alkalies by metals.

2. **Identifying the Process**: Hydrogen can be obtained through a process known as displacement. In this process, metals that are more reactive than hydrogen can displace hydrogen from its compounds.

3. **Displacement from Water**:
- When a reactive metal (like magnesium) is added to water, it reacts to form magnesium hydroxide and hydrogen gas.
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