A ballon is filled with `NO_(2)` gas. How will it behave as a lens for sound entering it from air ? Will it be converging or diverging ? What if the gas is now replaced with `H_(2)` gas ?

Explanation

To determine how a balloon filled with different gases behaves as a lens for sound, we need to analyze the properties of sound waves in relation to the density of the gases inside the balloon compared to the surrounding air.

### Step-by-Step Solution:

1. **Understanding the Concept of Sound Propagation**:
- Sound travels at different speeds in different media. The speed of sound is inversely proportional to the square root of the density of the medium. This means that as the density increases, the speed of sound decreases.

2. **Analyzing the Balloon Filled with NO₂**:
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