When rain is accompanied by a thunder storm, the collected rain water will have a \(\mathrm{pH}\) value (a) depending on the amount of dust in air. (b) slightly lower than that of rain water without thunderstorm. (c) slightly higher than that when the thunder storm is not there. (d) uninfluenced by occurrence of thunderstorm.

Thunderstorms are spectacular events that not only produce brilliant flashes of light in the sky but also play a lesser-known role in determining the chemical composition of rainwater. During a thunderstorm, the intense energy from lightning strikes initiates chemical reactions in the atmosphere. This influx of energy is powerful enough to break the strong triple bond between nitrogen molecules (N2) and the double bond between oxygen molecules (O2).

Once these bonds are broken, individual nitrogen and oxygen atoms are free to react with each other, forming various nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2). These are collectively known as NOx gases. The formation of NOx is a crucial step in altering the pH of rainwater because these gases will eventually dissolve in the moisture within clouds or falling raindrops.

The interaction becomes especially pronounced during thunderstorms due to the increased frequency of lightning strikes, which are the catalysts for these reactions. Consequently, thunderstorms are not just awe-inspiring natural events, but also chemical laboratories in the sky, with each bolt of lightning playing a role in the acidification of rainwater.

The chemistry behind thunderstorms and rainwater acidity is a marvel of nature's intricacies. As the nitrogen oxides (NO and NO2), which were formed due to lightning-induced reactions, start to cool and mix with water droplets in the atmosphere, they undergo further chemical changes. A notable product of these reactions is nitric acid (\text{HNO}_3), formed when nitrogen dioxide reacts with water according to the chemical equation:\[3\text{NO}_2 + \text{H}_2\text{O} \rightarrow 2\text{HNO}_3 + \text{NO}\]

This freshly produced nitric acid then dissolves in the remaining water vapor or raindrops, creating an acidic solution. The creation of nitric acid is significant because it's highly soluble in water, and once dissolved, it readily donates hydrogen ions (\text{H}^+), contributing to the acidity of the rainwater. Since the presence of hydrogen ions is the defining characteristic of an acidic solution, the more nitric acid there is, the more acidic the rainwater will become. Understanding this series of reactions is key to comprehending why rainwater can become significantly more acidic during a thunderstorm compared to a regular rain event.

Lightning is more than just a visual and auditory spectacle; it plays a critical role in chemistry that happens above us. The effects of lightning on rainwater pH can be profound. When lightning streaks through the atmosphere, the high temperatures and pressures it generates are enough to kick-start the formation of nitrogen oxides. These compounds are then available to dissolve in rainwater to form various acids, predominantly nitric acid.

The presence of these acids decreases the pH of rainwater, which is a numerical scale used to specify how acidic or basic a water-based solution is. Pure water has a pH of 7, which is considered neutral. However, rainwater generally has a pH slightly below 7 due to carbon dioxide from the atmosphere dissolving into it, forming carbonic acid. When lightning-induced acids like nitric acid enter the scene, they tip the balance even further, leading to a lower pH and a more acidic rainwater.

This impact on the rainwater's pH is critical for the environment, as acidic rain can have harmful effects on plant life, aquatic ecosystems, and infrastructure. Fortunately, nature also provides mechanisms, such as the buffering capacity of soils, to neutralize some of the acidity. Still, the subtle and sometimes not-so-subtle changes lightning brings to rainwater chemistry are impressive examples of the connection between atmospheric phenomena and environmental chemistry.