Which of the following is a non-conventional source of energy?

Lead is considered as

$BOD$ value of water is $20 \ ppm$. Then what can you conclude regarding water?

Biochemical Oxygen Demand,$(BOD)$ is a measure of organic material present in water. $BOD$ value less than $5 \ ppm$ indicates a water sample to be ..... .

What is the cause of the greenhouse effect?

Methemoglobinemia is caused by the presence of $X$ in drinking water. $X$ is