Identify the incorrect statement.

$CF_xCl_y$ (where $x + y = 4$). These compounds are not used because

Fill in the blanks:
$(1)$ Deficiency of fluoride is responsible for ............. .
$(2)$ The upper limit of lead concentration in drinking water is ............. .
$(3)$ The maximum limit of nitrate in drinking water is ............. .
$(4)$ ............. and ............. chemicals act as poisons for the nervous system.

Which of the following chemicals is not involved in photochemical smog formation?

$BOD$ stands for:

For your agricultural field or garden,you have developed a compost-producing pit. Discuss the process in the light of bad odour,flies,and recycling of wastes for a good produce.