Some reactions of $NO _2$ relevant to photochemical smog formation are

Identify $A , B , X$ and $Y$
In the given figure, the blocks $A$, $B$ and $C$ weigh $4\,\text{kg}$, $6\,\text{kg}$ and $8\,\text{kg}$ respectively. The coefficient of sliding friction between any two surfaces is $0.5$. The force $\vec{F}$ required to slide the block $C$ with constant speed is ___ N.
(Given: $g = 10\,\text{m s}^{-2}$) 
Method used for separation of mixture of products (B and C) obtained in the following reaction is: 
There is a number of factors that contribute to the pollution of the environment. Some of the major causes of atmospheric pollution are given below -