Which transition in the hydrogen spectrum would have the same wavelength as the Balmer type transition from $$\mathrm{n=4}$$ to $$\mathrm{n}=2$$ of $$\mathrm{He}^{+}$$ spectrum

Which one of the following statements is correct for electrolysis of brine solution?

Cobalt chloride when dissolved in water forms pink colored complex $$\underline{\mathrm{X}}$$ which has octahedral geometry. This solution on treating with conc $$\mathrm{HCl}$$ forms deep blue complex, $$\underline{\mathrm{Y}}$$ which has a $$\underline{\mathrm{Z}}$$ geometry. $$\mathrm{X}, \mathrm{Y}$$ and $$\mathrm{Z}$$, respectively, are

An organic compound 'A' with emperical formula $$\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}$$ gives sooty flame on burning. Its reaction with bromine solution in low polarity solvent results in high yield of B. B is