Question

The transition in He${}^{\oplus }$ ion that would have the same wavelength as the first Lyman line in hydrogen spectrum is :

• A. 2 $\to$ 1
• B. 5 $\to$ 3
• C. 4 $\to$ 2
• D. 6 $\to$ 4

Answer 1

The correct option is C 4 $\to$ 2

As we know,
$1/{\lambda }_H=R(1/1^2-1/2^2)$
for He, Z= 2
So for $4$ $\to$ $2$
$1/{\lambda }_{He}=R{2}^2(1/2^2-1/4^2)$ = $1/{\lambda }_H$