The energy released when gaseous hydrogen atoms combine together to form one of hydrogen
molecules is …………….. `KJ mol ^(-1)` .

Explanation

To find the energy released when gaseous hydrogen atoms combine to form hydrogen molecules (H₂), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The reaction involves two hydrogen atoms (H) combining to form one hydrogen molecule (H₂). The equation can be represented as:
\[
2H(g) \rightarrow H_2(g)
...