Oxyacids of chlorine show similarity in:

Which branch of science is associated with the development and cultivation of forests?

If the volume of a block of metal changes by $0.12 \%$ when it is heated through $20 ^oC$, the coefficient of linear expansion (in $^oC^{-1}$) of the metal is

From a disc of radius $R$,a concentric circular portion of radius $r$ is cut out so as to leave an annular disc of mass $M$. The moment of inertia of this annular disc about the axis perpendicular to its plane and passing through its centre of gravity is

If $u=\sin ^{-1}\left(\frac{x^2+y^2}{x+y}\right)$ then $x \frac{\partial u}{\partial x}+y \frac{\partial u}{\partial y}$ is equal to:

Two different radioactive elements with half-lives $T_{1}$ and $T_{2}$ have undecayed atoms $N_{1}$ and $N_{2}$ respectively,present at a given instant. The ratio of their activities at this instant is