Consumption of which one of the following foods can prevent the kind of blindness associated with vitamin-$A$ deficiency?

The molar heat capacity of water at constant pressure is $75 \ J \ K^{-1} \ mol^{-1}$. When $1 \ kJ$ of heat is supplied to $100 \ g$ of water,which is free to expand,the increase in temperature of water is ............... $K$.

$A$ wire in the form of a square of side $a$ carries a current $i$. Then,the magnetic induction at the centre of the square is (Magnetic permeability of free space $= \mu_0$)

Two wooden blocks of masses $M$ and $m$ are placed on a smooth horizontal surface as shown in the figure. If a force $P$ is applied to the system as shown in the figure such that the mass $m$ remains stationary with respect to the block of mass $M$, then the magnitude of the force $P$ is

The total number of $RNA$ strands in an animal virus is:

Which one of the following is used in the preparation of styrene?