Five point charges,each having magnitude $q$,are placed at the corners of a hexagon as shown in the figure. The net electric field at the centre $O$ is $\vec{E}$. To make the net electric field at $O$ equal to $6\vec{E}$,the charge to be placed on the remaining sixth corner should be: (in $q$)

$A$ ball of mass $1.2 \ kg$ moving with a velocity of $12 \ ms^{-1}$ makes a one-dimensional collision with another stationary ball of mass $1.2 \ kg$. If the coefficient of restitution is $\frac{1}{\sqrt{2}}$,then the ratio of the total kinetic energy of the balls after collision to the initial kinetic energy is:

The equation of the common tangent to the curves $y^2 = 8x$ and $xy = -1$ is

Verdigris is

Which one of the following statements is not correct?

In which of the following reactions does $H_2O_2$ act as a reducing agent?