Passengers travelling in an aeroplane are advised not to carry fountain pens because at higher altitudes,

Options

A. ink vapourizes due to high external pressure.
B. solidification of ink takes places due to very low external pressure.
C. pressure within the tube is more than the external pressure and causes leakage of ink.
D. pressure within the tube is lesser than the external pressure and causes leakage of ink.

Answer

### Step-by-Step Solution:

1. **Understanding the Environment in an Aeroplane:**
- When an aeroplane ascends to higher altitudes, the surrounding atmospheric pressure decreases significantly compared to sea level.

2. **Effect of Decreased Pressure:**
- The decrease in pressure affects the behavior of gases and liquids. In the case of a fountain pen, it relies on a specific pressure to function correctly.

3. **Functioning of a Fountain Pen:**
- A fountain pen works by drawing ink from its reservoir through a nib. This process is influenced by atmospheric pressure. At normal pressure, the ink flows smoothly due to the balance of pressure inside the pen and the external pressure.

4. **Impact of High Altitude on Fountain Pens:**
- At high altitudes, the reduced atmospheric pressure can disrupt the balance necessary for the ink to flow. This can lead to issues such as ink leaking out uncontrollably or the pen not writing at all.

5. **Conclusion:**
- Therefore, passengers are advised not to carry fountain pens on aeroplanes because the decrease in pressure at higher altitudes can cause malfunctioning of the pen, leading to potential mess or damage.