Select the correct pair from the following.

Vegetative propagation in mint occurs by

Which of the following substances is obtained from the fungus $Claviceps$ $\text{purpurea}$ (ergot)?

$A$ potentiometer consists of a wire of length $4\, m$ and resistance $10\,\Omega$. It is connected to a cell of $emf$ $2\, V$. The potential difference per unit length of the wire will be ............ $V/m$.

The speed of sound in oxygen $(O_2)$ at a certain temperature is $460 \; m/s$. The speed of sound in helium $(He)$ at the same temperature will be (assume both gases to be ideal): (in $; m/s$)

If $f(x) = \sqrt{ax} + \frac{a^2}{\sqrt{ax}}$,then $f^{\prime}(a)$ is equal to