World Environment Day is celebrated on

The greatest problem of water conservation is to reduce the amount of

The quantity of $CO_2$ in the atmosphere is about (in $\%$)

$A$: $El$ $Nino$ is a climatic change which causes deleterious environmental changes.
$R$: Increased tropospheric ozone due to $El$ $Nino$ causes a shift of climatic regions.

This award is given to individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.

Arrange the following in increasing order of their $BOD$ values: Sewage $(S)$,Distillery Effluent $(DE)$,Paper Mill Effluent $(PE)$,and Sugar Mill Effluent $(SE)$.