The perimeter of a sector is a constant. If its area is to be maximum,the sectorial angle is:

If $C$ is the midpoint of $AB$ and $P$ is any point outside $AB$,then:

The density of a mixture of $He$ and $O_2$ gases at $27 \, ^oC$ and $760 \, torr$ is found to be $0.543 \, g \, dm^{-3}$. What is the mass percentage of helium in the mixture?

In the given circuit,the readings of voltmeters $V_1$ and $V_2$ are $300 \, V$ each. The readings of the voltmeter $V_3$ and ammeter $A$ are respectively:

Among the following, the $CORRECT$ combinations are :
$A.$ $IF_3$ $\rightarrow$ $T$-shaped $(sp^3d)$
$B.$ $IF_5$ $\rightarrow$ Square pyramidal $(sp^3d^2)$
$C.$ $IF_7$ $\rightarrow$ Pentagonal bipyramidal $(sp^3d^3)$
$D.$ $ClO_4^-$ $\rightarrow$ Square planar $(sp^3d)$
Choose the correct answer from the options given below :

The horizontal and vertical displacements of a projectile at time $t$ are $x=36 t$ and $y=48 t-4.9 t^2$,respectively. Initial velocity of the projectile in $m/s$ is