Water samples with $BOD$ values of $4 \ ppm$ and $18 \ ppm$ respectively are:

Petroleum is a source of energy that is:

Given below are two statements:
Statement $I:$ Classical smog occurs in cool humid climate. It is a reducing mixture of smoke,fog and sulphur dioxide.
Statement $II:$ Photochemical smog has components,ozone,nitric oxide,acrolein,formaldehyde,$PAN$ etc.
In the light of above statements,choose the most appropriate answer from the options given below:

Methyl mercaptans are generated as waste from which industry?

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Sulphate	$I$. Pesticide
$B$. Fluoride	$II$. Bending of bones
$C$. Nicotine	$III$. Laxative effect
$D$. Sodium arsinite	$IV$. Herbicide

Choose the correct answer from the options given below.

How is excessive content of $CO_{2}$ responsible for global warming?