# Hydrogen $\;(_{1}H^{1})\;$ ,Deuterium $\;(_{1}H^{2})\;$ ,singly ionised Helium $\;(_{2}He^{4})^{+}\;$ and doubly ionized lithium $\;(_{3}Li^{6})^{++}\;$ all have one electron around the nucleus . Consider an electron transition from n=2 to n=1.If the wave lengths of emitted radiation are $\lambda_{1} ,\lambda_{2} ,\lambda_{3}\;$ and $\;\lambda_{4}\;$ respectively then approximately which one of the following is correct ?

$(a)\;4 \lambda_{1}=2 \lambda_{2}=2 \lambda_{3}=\lambda_{4}\qquad(b)\;\lambda_{1}=2 \lambda_{2}=2 \lambda_{3}=\lambda_{4}\qquad(c)\; \lambda_{1}=2 \lambda_{2}=2 4\lambda_{3}=9\lambda_{4}\qquad(d)\; \lambda_{1}=2 \lambda_{2}=2 3\lambda_{3}=4\lambda_{4}$