Question

It is observed that some of the spectral lines in hydrogen spectrum have wavelengths almost equal to those of the spectral lines in $H{e}^{+}$ ion, Out of the following the transitions in $H{e}^{+}$ that will make this possible is

• A. $n=3\text{to}n=1$
• B. $n=6\text{to}n=4$
• C. $n=5\text{to}n=3$
• D. $n=3\text{to}n=2$

Answer 1

The correct option is B $n=6\text{to}n=4$

Spectral energy for hydrogen and helium ions is shown below
For $H(n=3\text{to}n=2)\text{and}H{e}^{+}(n=6\text{to}n=4)$

corresponds to same energy. Hence $\lambda$ will be same.