If $b$ and $c$ are the lengths of the segments of any focal chord of a parabola $y^2 = 4ax$,then the length of the semi-latus rectum is:

The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is $2 ~s$. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

$A$ particle is projected from a point at an angle $\theta$ with the horizontal direction. At any time $t$,if $p$ is the linear momentum,$y$ is the vertical displacement,and $x$ is the horizontal displacement,which of the following graphs does $NOT$ represent the variation of kinetic energy $(KE)$ of the particle?

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

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

In the $Hoop$ process for the refining of $Al$,the molten materials form three different layers and remain separate during electrolysis because ..........

If $1, 2, 3$ and $4$ are the roots of the equation $x^4+ax^3+bx^2+cx+d=0$,then $a+2b+c$ is equal to