In an ellipse,the distance between its foci is $6$ and its minor axis is $8$. Then its eccentricity is

$A$ convex lens has its radii of curvature equal. The focal length of the lens is $f$. If it is divided vertically into two identical plano-convex lenses by cutting it,then the focal length of the plano-convex lens is ($\mu$ = the refractive index of the material of the lens).

How many moles of $KMnO_4$ are required to oxidize $1 \ mol$ of $FeC_2O_4$ in an acidic medium?

With what minimum velocity should a block of mass $m$ be projected from the left end $A$ towards end $B$ such that it reaches the other end $B$ of a conveyor belt of length $L$ moving with a constant velocity $v$ in the opposite direction? The friction coefficient between the block and the belt is $\mu$.

$A$ particle of mass $m$ and charge $q$ moves with a constant velocity $v$ along the positive $x$-direction. It enters a region containing a uniform magnetic field $B$ directed along the negative $z$-direction,extending from $x = a$ to $x = b$. The minimum value of $v$ required so that the particle can just enter the region $x > b$ is

Which of the following substances is known as lead sugar?