Which of the following species has no $p\pi - p\pi$ bond but has a bond order equal to that of $O_2$?

With respect to chlorobenzene,which of the following statements is not correct?

$A$ rod $P$ of length $1 \ m$ is hinged at one end $A$ and there is a ring attached to the other end. Another long rod $Q$ is hinged at $B$ and it passes through the ring. The rod $P$ is rotated about an axis which is perpendicular to the plane in which both the rods are present and the variation between the angles $\theta$ and $\phi$ are plotted as shown. The distance between the hinges $A$ and $B$ is ....... $m$.

Select the taxon mentioned that represents both marine and fresh water species.

If $f(x)=2 x^4-13 x^2+a x+b$ is divisible by $x^2-3 x+2$,then $(a, b)$ is equal to

Total internal reflection of light is possible when light enters from