The ratio for the speed of the electron in the 3 ^ rd orbit of He ^...

The speed of electron is given by $v = 2 . 18 \times {10}^{6} \times \dfrac{Z}{n}m{s}^{- 1}$, where, $Z$ is atomic number and $n$ is number of orbit.

Now, for third orbit, ratio of speed of electron is $\dfrac{{v}_{H}}{v{He}^{+}} = \dfrac{{Z}_{H}}{Z{He}^{+}} = \dfrac{1}{2}$

$⇒ \dfrac{v{He}^{+}}{{v}_{H}} = \dfrac{2}{1}$