State whether the following statements are true or false:
$(1)$ The concentration of oxygen in cold water is $100 \ ppm$.
$(2)$ If the concentration of dissolved oxygen in water is less than $6 \ ppm$,the growth of fish gets inhibited.

The poisonous gas that is released during the combustion of petrol in a car engine is

How can you apply Green Chemistry for the following?
$(a)$ To reduce photochemical smog.
$(b)$ To avoid the use of chlorinated solvents and chlorinated bleaching agents in dry cleaning.
$(c)$ To reduce the use of synthetic detergents.
$(d)$ To reduce the consumption of petrol and diesel.

Write down the reactions involved during the formation of photochemical smog.

The enamel present on teeth becomes much harder due to the conversion of $[3 Ca_3(PO_4)_2, X]$ into $[3 Ca_3(PO_4)_2, Y]$. What are $X$ and $Y$?

The photochemical smog does not generally contain.