Excess of fluoride in drinking water causes mottling of teeth. Mottling of teeth, also known as dental fluorosis, occurs when there is a high concentration of fluoride during the development of teeth, leading to white or brown discoloration and pitted enamel. This condition is primarily a cosmetic issue and does not usually affect the function or health of the teeth.
Lung disease (option 1) is not caused by excess fluoride in drinking water. Lung diseases can be caused by various factors such as smoking, infections, and environmental pollutants.
Intestinal infection (option 2) is also not caused by excess fluoride. Intestinal infections are typically caused by bacteria, viruses, parasites, or other pathogens that enter the digestive system through contaminated food or water.
Option 4 states that no option is correct, but this is incorrect. The correct answer is option 3 - mottling of teeth.