The total number of valence electrons in $4.2 \, g$ of $N_3^-$ ion is ......... $N_A$. ($N_A$ = Avogadro number)

The area (in square units) of the region enclosed by the two circles $x^2+y^2=1$ and $(x-1)^2+y^2=1$ is

If $f(x) = \sqrt{ax} + \frac{a^2}{\sqrt{ax}}$,then $f^{\prime}(a)$ is equal to

Which of the following is an example of a heterogeneous catalysis reaction?

If you are asked to classify the various algae into distinct groups,which of the following characters should you choose?

$A$ line segment $AM = a$ moves in the $XOY$ plane such that $AM$ is parallel to the $X$-axis. If $A$ moves along the circle $x^2 + y^2 = a^2$,then the locus of $M$ is