What is the intensity of sound in normal conversation?

Catalytic converters,which have expensive metals as catalysts,are fitted into automobiles for reducing emission of poisonous gases. Which of the following is $NOT$ used in them?

Identify $X$ and $Y$ from the figure representing an Electrostatic Precipitator:
$X-Y$

The most hazardous metal pollutant of automobile exhaust is

High $BOD$ indicates $........$.

Electrostatic Precipitator $(ESP)$:
$I.$ Is an electrical device to remove particulate matter present in the exhaust of thermal power plant.
$II.$ More than $99\, \%$ particulate matter can be removed by this method.
$III.$ $ESP$ has electrode wires and a stage of collecting plates.
Which of the statements given above are correct?