How is the presence of `SO_2` detected?

Explanation

To detect the presence of sulfur dioxide (SO₂), we can use both physical and chemical methods. Here’s a step-by-step explanation of each method:

### Step-by-Step Solution:

**Step 1: Physical Detection Method**
- **Characteristic Property**: SO₂ is known for its distinct physical properties. The most notable is its pungent smell.
- **Detection**: One can detect the presence of SO₂ simply by smelling it. It is important to note that this should be done with caution, as inhaling SO₂ can be harmful.

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