The radiant energy from the sun incident normally at the surface of the earth is $20 \ kcal/m^2-min$. What would have been the radiant energy incident normally on the earth if the sun had a temperature twice of the present one? (in $kcal/m^2-min$)

In Van der Waals equation of state for a non-ideal gas,the term that accounts for intermolecular forces is

Which of the following species has the highest electron affinity?

Which among the following reactions will take place spontaneously?

$A$ particle carrying a charge equal to $100$ times the charge on an electron is rotating per second in a circular path of radius $0.8 \ m$. The value of the magnetic field produced at the centre will be (where ${\mu _0}$ is the permeability of vacuum).

As shown in the figure,a block of mass $10 \, kg$ lying on a horizontal surface is pulled by a force $F$ acting at an angle of $30^{\circ}$ with the horizontal. For $\mu_{s} = 0.25$,the block will just start to move for the value of $F$ in $N$ is: [Given $g = 10 \, ms^{-2}$]