The cooking gas cylinder is filled with .......

Match the following and choose the correct combination from the options given:
Column $I$ | Column $II$
$(1)$ $DDT$ | $(p)$ $CO, CO_2$
$(2)$ $PAN$ | $(q)$ Smog
$(3)$ Acid rain | $(r)$ Biological magnification
$(4)$ Global warming | $(s)$ $SO_2$

In which of the following is the concentration of $DDT$ highest?

$5^{th}$ June is celebrated as.....

Which of the following plants is used for the purification of water?

At the beginning of the twentieth century,forests covered about ........... of the land area of India. (in $\%$)