The brown color of photochemical smog is primarily due to which of the following?

Choose the incorrect statement.

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

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ Photochemical smog causes cracking of rubber.
Reason $(R):$ Presence of ozone,nitric oxide,acrolein,formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.
Choose the most appropriate answer from the options given below:

The part of the Earth where life exists,known as the biosphere,is composed of which components?

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.