In which of the following reactions does the hybridisation of the central atom change from $sp^2$ to $sp^3$?

Spirochetes are ........

If $f(1)=1$ and $f^{\prime}(1)=3$,then the derivative of $f(f(f(x)))+(f(x))^2$ at $x=1$ is

$\int \frac{\sin x+8 \cos x}{4 \sin x+6 \cos x} d x$ is equal to

$A$ rod of length $L$ is held vertically on a smooth horizontal surface. The top end of the rod is given a gentle push. At a certain instant of time,when the rod makes an angle $\theta$ with the horizontal,the velocity of the $COM$ of the rod is $v_0$. The velocity of the end of the rod in contact with the surface at that instant is: