Green glands,present in some arthropods,help in

What is the percentage of lead in a lead pencil (in $,\%$)?

The product of the lengths of perpendiculars drawn from any point on the hyperbola $x^2 - 2y^2 - 2 = 0$ to its asymptotes is:

Who among the following is known as the 'Father of Taxonomy'?

$A$ ray of light refracts from medium $1$ into a thin layer of medium $2$,crosses the layer,and is incident at the critical angle on the interface between medium $2$ and $3$ as shown in the figure. If the angle of incidence of the ray is $\theta$,the value of $\theta$ is

Which one of the following statements is wrong?