$A$ magnetic needle lying parallel to a magnetic field is turned through $60^{\circ}$. The work done on it is $W$. The torque required to maintain the magnetic needle in the position mentioned above is

$A$ monoatomic ideal gas,initially at temperature $T_1$,is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature $T_2$ by releasing the piston suddenly. If $L_1$ and $L_2$ are the lengths of the gas columns before and after the expansion respectively,then the ratio $\frac{T_2}{T_1}$ is:

The rate of disintegration of a fixed quantity of a radioactive element can be increased by

The shortest distance between the line $y-x=1$ and the curve $x=y^2$ is

In a haplontic life cycle,how many of the four haploid nuclei degenerate?

Which one of the following oxides is reduced by water gas to obtain the metal during its extraction?