Which of the following compounds does not react with $NaNO_2$ and $HCl$?

The probability that a number selected at random from the set of numbers ${1, 2, 3, \ldots, 100}$ is a cube,is

Isogamous condition with non-flagellated gametes is found in:

An achromatic combination of lenses produces

Which of the following is the correct order of basic strength?

$A$ 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.