The contribution in the total current flowing through a semiconductor due to electrons and holes are $3/4$ and $1/4$ respectively. If the drift velocity of electrons is $5/2$ times that of holes at this temperature,then the ratio of concentration of electrons and holes is

Two polaroids are placed in the path of an unpolarized beam of intensity $I_0$ such that no light is emitted from the second polaroid. If a third polaroid,whose polarization axis makes an angle $\theta$ with the polarization axis of the first polaroid,is placed between these polaroids,then the intensity of light emerging from the last polaroid will be:

Which one of the following elements reduces $NaOH$ to $Na$?

What is zeolite among the following?

Five identical springs are used in the following three configurations. The time periods of vertical oscillations in configurations $(i)$,$(ii)$ and $(iii)$ are in the ratio:

The value of $\int_{-1}^{1} (\sqrt{1 + x + x^2} - \sqrt{1 - x + x^2}) \, dx$ is