Environmental Issues

• Toxic heavy metals from industries that cause water pollution, such as lead, mercury, and cadmium, typically have a density of more than 5 g/cm³.
• These metals are denser than water, making them sink and concentrate in water bodies, contributing to pollution.

The correct answer is (B) : more than 5 g/cm³.

BOD (Biochemical Oxygen Demand) is a measure of the amount of oxygen required by microorganisms to decompose the organic matter in a water sample. Higher BOD values indicate higher pollution levels because more oxygen is consumed to break down organic waste.

• 0.16 mg/L: This is a low BOD value, indicating less pollution and relatively clean water.
• 0.6 mg/L: This is still a moderate value, suggesting slightly polluted water.
• 0.06 mg/L: This is the lowest among the options, showing very low pollution levels.
• 6 mg/L: This is a very high BOD value, indicating that the water sample has a large amount of organic matter that is being decomposed by microorganisms, signifying high pollution levels.

Thus, the water sample with a BOD value of 6 mg/L is the most polluted among the given options.

The correct answer is (D) : 6 mg/L.