The whorl of bracts present below the inflorescence of $Helianthus$ $(sunflower)$ is

What is the use of Guayule ($Parthenium$ $argentatum$)?

$\int_0^1 x^{3/2} \sqrt{1-x} \, dx$ is equal to

Two bodies of masses $m$ and $4m$ are placed at a distance $r$. The gravitational potential at a point on the line joining them,where the gravitational field is zero,is

Let $A(3-i)$ and $B(2+i)$ be two points in the Argand plane. If the point $P$ represents the complex number $z=x+iy$,which satisfies $|z-3+i|=|z-2-i|$,then the locus of the point $P$ is

Explain why alkyl groups act as electron donors when attached to a $\pi$ system.