The tail of a comet is the longest when:

Options

A. It is nearest to the Sun
B. It is farthest from the sun
C. It is far from the earth
D. It is near Saturn

Explanation

**Step-by-Step Solution:**

1. **Understanding Comets**: Comets are celestial bodies made of ice, dust, and rocky material. They have a nucleus that can be several kilometers in diameter.

2. **Movement of Comets**: Comets travel in elliptical orbits around the Sun. As they approach the Sun, they experience changes due to solar radiation and solar wind.

3. **Effect of the Sun's Heat**: When a comet gets closer to the Sun, the heat causes the ice in the comet to vaporize. This process is known as sublimation, where solid ice turns directly into gas.

4. **Formation of the Tail**: The vaporized gases, along with dust and other particles, are released from the comet. This creates a glowing coma around the nucleus and forms a tail that points away from the Sun.

5. **Length of the Tail**: The tail of a comet is longest when it is closest to the Sun because the increased heat causes more ice to vaporize, resulting in a larger amount of gas and dust being expelled.

6. **Conclusion**: Therefore, the tail of a comet is longest when the comet is nearest to the Sun.

**Final Answer**: The tail of a comet is the longest when it is closest to the Sun.

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