posted by bun .
the shortest and longest wavelength series in singly ionized helium is 22.8nm and 30.4nm . Are they right?
How many orders we can see between the angles range observations 30 and 90 in the Balmer's series?
These look like questions asked in conjunction with some lab experiment.
Singly-ionized helium, which has a hydrogenlike spectrum, would have more than two wavelength series, just as hydrogen does. The shortest wavelength series limit would be at 1/4 of the Lyman series wavelength of hydrogen, or at 22.7 nm . A wavelength of 30.4 nm would correspond to the Balmer series, but there are others at longer wavelengths.
The answer to your second question depends upon the diffraction grating that was used. I have no idea what experiment is being talked about. Are you writing a lab report for an experiment you did not witness?