Why does a balloon expand when taken to a higher elevation, assuming the temperature remains constant?

• A. The external air pressure decreases, allowing the gas inside the balloon to expand.
• B. The number of gas molecules inside the balloon increases at higher elevation.
• C. The gas inside the balloon cools down, causing it to expand.
• D. The volume of the balloon decreases because the pressure inside increases.

Answer: (A)

Verified step by step guidance

1. Recall the relationship between pressure and volume for a gas at constant temperature, described by Boyle's Law: \(P \times V = \text{constant}\), where \(P\) is pressure and \(V\) is volume.
2. Understand that as the balloon is taken to a higher elevation, the external atmospheric pressure decreases because air pressure decreases with altitude.
3. Since the temperature is constant and the number of gas molecules inside the balloon remains the same, the gas inside the balloon must respond to the lower external pressure.
4. According to Boyle's Law, if the external pressure decreases, the volume of the gas must increase to keep the product \(P \times V\) constant.
5. Therefore, the balloon expands because the lower external pressure allows the gas inside to occupy a larger volume.