Which of the following is a secondary pollutant?

$A$ sinusoidal voltage of peak value $200\, V$ is connected to a diode and resistor $R$ in the circuit shown so that half-wave rectification occurs. If the forward resistance of the diode is negligible compared to $R$,the $rms$ voltage across $R$ is approximately.....$V$.

$A$ concave mirror of focal length $f$ produces an image $n$ times the size of the object. If the image is real,then the distance of the object from the mirror is:

What is common among silverfish,scorpion,crab,and honeybee?

Which process is used to obtain products like cheese and yogurt?

$X$ being a higher category is the assemblage of families which exhibit a few $Y$ characters. The $Z$ characters are less in number as compared to different genera included in a family. Identify $X$,$Y$,and $Z$.