The primary cause of rainwater around the world having a pH lower than 7 isa.Bromineb.Methanec.carbon dioxided.sulfur dioxide

The primary cause of rainwater around the world having a pH lower than 7 is sulfur dioxide. Here's why:

1. When sulfur dioxide (SO2) is released into the atmosphere, it can react with water (H2O) to form sulfurous acid (H2SO3). This is a weak acid, but it does contribute to the acidity of rainwater.

2. Sulfur dioxide is primarily released through human activities, such as the burning of fossil fuels (coal and oil) and the smelting of mineral ores that contain sulfur.

3. In addition to this, natural processes like volcanic eruptions also release sulfur dioxide into the atmosphere.

4. Once in the atmosphere, sulfur dioxide can be transported long distances by wind currents, where it eventually falls as acid rain.

5. This acid rain has a pH lower than 7, which is considered acidic. Normal, clean rain has a pH of about 5.6, which is slightly acidic due to the presence of carbon dioxide. However, when sulfur dioxide is added to the mix, the pH can drop even lower.

So, the correct answer is d. sulfur dioxide.