JEE Advanced levelSingle correct optionDifficulty 3 of 3as093
A line in the HeX+ spectrum coincides in wavelength with the n=3→n=2 line of hydrogen. This HeX+ transition is
An=4→n=3
Bn=5→n=3
Cn=6→n=4
Dn=6→n=3
Answer: C
Hydrogen 3→2: R(1/4−1/9)=5R/36=0.1389R. For HeX+, 6→4 gives 4R(1/16−1/36)=4R×5/144=0.1389R, a match. The others give 0.194R (4→3), 0.284R (5→3) and 0.333R (6→3).