In an $NPN$ transistor,$10^{10}$ electrons enter the emitter region in $10^{-6} \, s$. If $2\%$ of electrons are lost in the base region,then the collector current and the current amplification factor $(\beta)$ are,respectively:

Which one has the maximum oxidation number of phosphorus?

$A$ bi-convex lens is formed with two thin plano-convex lenses as shown in the figure. The refractive index of the first lens is $1.5$ and that of the second lens is $1.2$. Both the curved surfaces have the same radius of curvature $R = 14\; cm$. For this bi-convex lens,if the object distance is $40\; cm$,the image distance will be: (in $; cm$)

The refractive index of a material of a plano-concave lens is $5/3$,and the radius of curvature is $0.3 ~m$. The focal length of the lens in air is (in $~m$)

$A$ random variable $X$ has the probability distribution given below. Its variance is

$X$	$1$	$2$	$3$	$4$	$5$
$P(X=x)$	$k$	$2k$	$3k$	$2k$	$k$

$A$ square of side $3\;cm$ is placed at a distance of $25\;cm$ from a concave mirror of focal length $10\;cm$. The centre of the square is at the axis of the mirror and the plane is normal to the axis. The area enclosed by the image of the square is $......\;cm^2$.