The $Adaptation$ of eyes in the dark is due to

What is the product formed when phenol reacts with concentrated $HNO_3$?

Which of the following is a secondary pollutant?

In free space,a shell moving with velocity $60\,m/s$ along the positive $x$-axis explodes into two pieces of mass ratio $1:2$ when it passes through the origin. After the explosion,the velocity of the centre of mass is ........ $m/s$.

If the difference between the roots of the equation $x^2 + ax + 1 = 0$ is less than $\sqrt{5}$,then what is the set of possible values of $a$?

$A$ cell of $emf$ $E$ has an internal resistance $r$ and is connected to a rheostat. When the resistance $R$ of the rheostat is changed,which is the correct graph of the potential difference $V$ across it?