A trail is created by jet-planes as they release through the exhaust.

Options

A. Carbon dioxide
B. Water vapours
C. Carbon monoxide
D. Hydrogen

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Jet Plane Trail**: When a jet plane flies, it releases exhaust gases from its engines. This exhaust includes various components, one of which is water vapor.

2. **Formation of Water Vapor**: The water vapor is created when the fuel burns in the jet engine. As the plane ascends, the temperature and pressure conditions change, allowing the water vapor to be released into the atmosphere.

3. **Condensation Process**: Once the water vapor is released, it can cool down quickly in the upper atmosphere. This cooling causes the water vapor to condense into tiny water droplets or ice crystals, depending on the temperature.

4. **Cloud Formation**: The condensed water droplets or ice crystals cluster together, forming a visible cloud. This cloud appears as a white streak in the sky, which is often referred to as a contrail (short for condensation trail).

5. **Comparison to Hot Breath**: This phenomenon is similar to what happens when a person exhales on a cold day. The warm, moist air from the lungs meets the cold air outside, causing the moisture to condense and form a visible cloud of breath.

6. **Identifying the Correct Option**: In the context of the question, we need to identify what the trail consists of. The options given are:
- Carbon Dioxide
- Water Vapor
- Carbon Monoxide
- Hydrogen

Since we established that the trail is primarily made up of water vapor, the correct answer is "Water Vapor."

**Final Answer**: The trail created by jet planes is primarily made up of **Water Vapor**.

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