$A$ glass convex lens is of refractive index $1.55$ with both faces of same radius of curvature. What will be the radius of curvature if the focal length is to be $20 \text{ cm}$ (in $text{ cm}$)?

In which activities other than studies should the energy of boys be utilized?

Charges are placed on the vertices of a square as shown. Let $\overrightarrow{E}$ be the electric field and $V$ be the electric potential at the centre. If the charges on $A$ and $B$ are interchanged with those on $D$ and $C$ respectively,then:

Which is the major product of the following reaction?

The chemical reaction that involves the roasting process is

The mean of the numbers obtained on throwing a die having $1$ on three faces,$2$ on two faces,and $5$ on one face is