Question in the image, please give explanation also, irrelevant answers would be reported, please solve it asap

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.

Answer trigonal pyramidal;

3-isopentane; 3-methylbutane, and 1,2-methylpropane do not meet iupac rules, so they are wrong names.the only valid name onthe list is 2-methylbutane, which is the same isopentane.this is its formula:                   ch2                    |ch3 - ch - ch2 - ch3answer: 2-methylbutane

The correct answer is b)