Which one of the following is not used in organic farming?

Which valve is located between the right atrium and the right ventricle?

Particles of masses $m, 2m, 3m, \ldots, nm$ grams are placed on the same line at distances $l, 2l, 3l, \ldots, nl$ $cm$ from a fixed point. The distance of the centre of mass of the particles from the fixed point in centimetres is

$A$ parallel plate capacitor with air as medium between the plates has a capacitance of $10\,\mu F$. The area of the capacitor is divided into two equal halves and filled with two media as shown in the figure having dielectric constants $k_1 = 2$ and $k_2 = 4$. The capacitance of the system will now be.......$\mu F$.

If $\overline{a}, \overline{b}, \overline{c}$ are non-coplanar unit vectors such that $\overline{a} \times (\overline{b} \times \overline{c}) = \frac{\overline{b} + \overline{c}}{\sqrt{2}}$,then the angle between $\overline{a}$ and $\overline{b}$ is

Which of the following regulates blood pressure and heart rate?