The orbital angular momentum of a $3p$ electron is

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

$A$ conducting rod with resistance $r$ per unit length is moving inside a vertical magnetic field $\vec B$ at constant speed $v$ on two horizontal parallel ideal conductor rails. The ends of the rails are connected to a resistor $R$. The separation between the rails is $d$. The rod maintains a tilted angle $\theta$ to the rails. Find the external force required to keep the rod moving.

The length of the common chord of the circles of radii $15$ and $20$,whose centers are $25$ units of distance apart,is

The major product of the following reaction is

$Assertion (A)$: van der Waals' forces are responsible for chemisorption. $Reason (R)$: High temperature is favourable for chemisorption. The correct answer is