A hydrogen-filled balloon expands as it rises and may even burst after rising very high in the atmosphere. This happens because
A. The temperature increases with height
B. The temperature decreases with height
C. The atmospheric pressure increases with height
D. The atmospheric pressure decreases with height

Hint: The pressure is directly proportional to the atmospheric weight. Even, the pressure is inversely proportional to the height, that is, distance from the ground. Using these two relations, the answer to this question can be found easily.

Complete answer:
The main point to remember is that the existence of the atmospheric pressure is due to the weight of the gases present in the atmosphere, but at a certain height from the ground (the surface of the earth), this pressure reduces.

A hydrogen-filled balloon, of course, refers to a balloon that is filled with the gas. This gas present inside the balloon also creates pressure inside the balloon.
At the ground level, the pressure inside the balloon will be balanced by the pressure present outside, that is, the atmospheric pressure due to the weight of the gases present in the atmosphere.
As the balloon starts to rise, the atmospheric pressure reduces as the distance of the balloon from the ground increases. This decrease in the atmospheric pressure imbalances the equilibrium of the balloon, in turn, forces the pressure present inside the balloon to rise, in order to attain the equilibrium lost.
As the pressure inside the balloon increases, the balloon starts to expand. This process of expansion of the balloon continues until the balloon tries to reach the equilibrium state.
But, with the increase in the height of the balloon, the atmospheric pressure keeps on decreasing and never allows the balloon to reach the equilibrium.
At some point, the balloon bursts, because of the extreme increase in the pressure inside.

So, the correct answer is “Option D”.

Note:
The things to be on your finger-tips for further information on solving these types of problems are: The atmospheric pressure and the distance from the ground are inversely proportional to each other. Even, the pressure inside the balloon is different from that of the atmospheric pressure, as, the atmospheric pressure decreases with the increase in height, whereas, the inside pressure increases with the increase in height.