Which nitrogenous base is present in $RNA$ but not in $DNA$?

Which one of the following statements is $WRONG$ in the context of $X-$rays generated from an $X-$ray tube?

In good conductors of electricity,the type of bonding that exists is

The intensity of radiation emitted by the sun has its maximum value at a wavelength of $510 \ nm$ and that emitted by the north star has the maximum value at $350 \ nm$. If these stars behave like black bodies,then the ratio of the surface temperature of the sun and north star is

$A$ particle $P$ is moving in a circle of radius $a$ with a uniform speed $v$. $C$ is the centre of the circle and $AB$ is a diameter. When passing through $B$,the angular velocity of $P$ about $A$ and $C$ are in the ratio:

If $\tan x + \tan \left(x + \frac{\pi}{3}\right) + \tan \left(x + \frac{2\pi}{3}\right) = 3$,then $\tan 3x$ is equal to