$\int\left(\sqrt{\frac{a+x}{a-x}}+\sqrt{\frac{a-x}{a+x}}\right) d x$ is equal to

$A$ particle of mass $10\, g$ is kept on the surface of a uniform sphere of mass $100\, kg$ and radius $10\, cm$. Find the work to be done against the gravitational force between them to take the particle far away from the sphere (you may take $G = 6.67 \times 10^{-11}\, N m^2/kg^2$).

Sertoli cells are regulated by the pituitary hormone known as:

The arrangement of $X^{-}$ ions around $A^{+}$ ion in solid $AX$ is given in the figure. If the radius of $X^{-}$ is $250 \ pm$,the radius of $A^{+}$ is ............. $pm$.

$A$ plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If the lenses are made of different materials with refractive indices $\mu_1$ and $\mu_2$ and $R$ is the radius of curvature of the curved surface of the lenses,then the focal length of the combination is:

For better survival of the human population,which of the following steps is most important?