<u>Answer:</u> The correct answer is Option C.
<u>Explanation:</u>
As we move higher in the sky, the atmospheric pressure decreases. The relationship of pressure with volume is given by Boyle's Law.
This law states that the pressure of the gas is inversely proportional to the volume of the gas at constant temperature.
Mathematically,
where,
P is the pressure of the gas.
V is the volume of the gas.
If the pressure of the gas decreases, the volume increases and vice-versa.
As written above, the pressure at higher levels decreases, which results in the increase of volume. Hence, the balloon expands.
therefore, the correct answer is option C.