Which transition in He+ emits radiation of the same wavelength as the n=2-> n=1 line of hydrogen?

JEE Main levelSingle correct optionDifficulty 2 of 3as076

Which transition in $He X^{+}$ emits radiation of the same wavelength as the $n = 2 \to n = 1$ line of hydrogen?

For

He X^{+}

1/ λ = 4 R (1/ n_{f}^{2} - 1/ n_{i}^{2})

. For

4 \to 2

this is

4 R \times 3/16 = 3 R /4

, equal to hydrogen's

R (1 - 1/4) = 3 R /4

. The others give

3 R

32 R /9

and

5 R /9