The technique used to make numerous copies of a specific segment of $DNA$ quickly and accurately is

Two gases $A$ and $B$ having the same volume,effuse through an orifice in $30 \ min$ and $10 \ min$ respectively. The molar mass of $A$ is $162$. The molar mass of $B$ will be

$A$ charge $q$ is placed at the centre of the line joining two equal charges $Q$. The system of the three charges will be in equilibrium if $q$ is equal to:

Two spherical soap bubbles of radii $r_1$ and $r_2$ in vacuum combine under isothermal conditions. The resulting bubble has a radius equal to:

$A$ cylindrical conductor of radius $R$ carries a current $i$. The value of the magnetic field at a point which is $R/4$ distance inside from the surface is $10 \ T$. Find the value of the magnetic field at a point which is $4R$ distance outside from the surface.

Which of the following equilibria will shift to the right side on increasing the temperature?