Which of the following is/are estimated by tura polluted water with potassium dichromate solution in acidic medium?

$$ \begin{array}{c|c|c} \hline \text { COD } & \text { BOD } & \text { DO } \\ \hline \text { I } & \text { II } & \text { III } \\ \hline \end{array} $$

The BOD values for pure water and highly polluted water are respectively.

An metal catalyst $(X)$ is used in the catalytic converter of automobiles. This prevents the release of gas $Y$ into the atmosphere. What are $X$ and $Y$ respectively?

$$ \text { Match the following. } $$

List-I F-ion concentration in drinking water)		List-II (Effects on humans)
A	$$ \text { <1 ppm } $$	I	$$ \text { Harmful to bones } $$
B	$$ >2 \mathrm{ppm} $$	II	$$ \text { Tooth decay } $$
C	$$ >10 \mathrm{ppm} $$	III	$$ \text { Brown mottling of teeth } $$

$$ \text { Correct answer is } $$