Very pure hydrogen (99.9%) can be made by which of the following processes ?

Explanation

To determine how very pure hydrogen (99.9%) can be made, we can analyze the process described in the video transcript. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Process
The process mentioned for obtaining very pure hydrogen is the reaction of water with salt hydrides. An example of a salt hydride is sodium hydride (NaH).

### Step 2: Write the Chemical Reaction
The chemical reaction that occurs when sodium hydride reacts with water can be written as:
\[ \text{NaH} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \]
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