In a solid, $\mathrm{B}^{-}$ions occupy corners of a cube forming ccp structure. If $\mathrm{A}^{+}$ion occupy half the tetrahedral voids, formula of the solid is

Calculate the radius of first orbit of He$^+$.

Identify reagent 'A' used in the following reaction?

Acidic buffer solution is prepared by mixing proportionate quantity of