Question

When rain is accompanied by a thunderstorm, the collected rain water will have a $pH$ value
A. uninfluenced by occurrence of thunderstorm
B. depending on the amount of dust in air
C. slightly lower than that of rain water without thunderstorm
D. slightly higher than that when the thunderstorm is not there

Answer 1

When rain is accompanied by a thunderstorm, some of the acids get dissolved in the rain water itself. During the thunderstorm, the air gets ionized and transfer of electrons takes place in the air which causes a reaction between the available gases and the water molecules in the atmosphere.

Complete answer:
When the water molecules in the atmosphere during the rain come in contact with the thunderstorm, they get ionized in such a way that the total electrical neutrality of the water molecules gets distorted due to a distortion in the electron cloud of the water molecule. In the atmosphere, various other gases are present such as sulfur dioxide, carbon dioxide, carbon monoxide, nitrous and nitric oxide, etc. The energy during a thunderstorm is sufficient to ionize these gases as well and as a result of which, these gases start dissolving in the water molecules as they react with the freely available protons. These reactions produce various acids such as nitric acid, sulfuric acid, carbonic acid, etc and precipitate along with the rainfall. Due to the presence of some acid content in rainfall, its $pH$ value is slightly lower than the rain water without thunderstorm.

Thus, the correct option is C. Slightly lower than that of rain water without thunderstorms.

Note:
This process of ionization of rain water which enables it to dissolve the gases of the atmosphere is employed in the production of acid rain which is a harmful effect as it corrodes the calcium carbonate structures and makes the soil and water bodies acidic in nature and not habitual for the living organisms residing there.