The correct order of the $O-O$ bond length in $O_2$,$H_2O_2$ and $O_3$ is

$A$ compound absorbs light in the wavelength region $490-500 \ nm$. Its complementary colour is

$A$ thin circular ring of mass $M$ and radius $r$ is rotating about its axis with a constant angular velocity $\omega$. Four particles,each of mass $m$,are gently placed on the ring at opposite points of two perpendicular diameters. The new angular velocity of the ring will be:

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

Fungal herbicides are produced by which of the following?

$A$ lens of power $+2 \text{ diopters}$ is placed in contact with a lens of power $-1 \text{ diopter}$. The combination will behave like: