Aldehydes are produced in the atmosphere by:

What is the percentage of oxygen by volume in dry air (in $\%$)?

Fill in the blanks:
$(1)$ Hydrocarbon compounds are made from ........ and ........ .
$(2)$ ........ has a capacity to stop the flow of oxygen.
$(3)$ ........ is formed by attaching carbon monoxide with hemoglobin in blood.

Environmental pollution is the effect of undesirable changes in the properties of our air,land,water,or soil that may harmfully affect...

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

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 $SO_2$