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

Mention the main causes for water pollution.

Identify the air pollutant which in high concentration leads to stiffness of flower buds?

The incorrect statement from the following is:

Identify the correct statements from the following:
$a$) $BOD$ value of clean water is less than $5 \ ppm$
$b$) Oxidation of ethene in the presence of $Pd^{2+}$ catalyst in aqueous medium gives acetic acid
$c$) Photochemical smog causes damage to plant life
$d$) Reducing smog is a mixture of smoke,fog and $SO_2$

Which one of the following gases is reported to retard photosynthesis?