The middle lamella of a plant cell is primarily composed of which of the following?

$\int \frac{dx}{\sqrt{x-x^2}}$ is equal to

Which is the most widely cultivated fiber-yielding crop in India?

The Earth $E$ moves in an elliptical orbit with the Sun $S$ at one of the foci as shown in the figure. Its speed of motion will be maximum at the point:

Tetrahalides of group $14$ elements (except that of carbon) act as

Male cockroach can be identified from the female by the presence of