Hydrogen has four emission lines in the visible light range : violet, blue, green, and red. match the color of the emission line to its electron transition.

a. n =  4     →   n =  2 
b. n =  3     →   n =  2
c. n =  6    →   n =  2
d. n =  5    →   n =  2 

C.    n = 6   →   n = 2     Violet

D.    n = 5   →   n = 2     Blue

A.    n = 4   →   n = 2     Green

B.    n = 3   →   n = 2     Red

Explanation:

The transitions involved are all to energy level n=2  from higher energy levels. The energy of the emission line correspondingly will reflect a higher energy the greater n is and the color of the emission spectra line will likewise correspond to higher energy. Since the energy of the colors given  follow the sequence:

Remember that the the energy and the frequency of the visible colors is greatest for violet and lowest for red. That is why we refer  to ultraviolet light being highly energetic ( sunburn) and infrared gogles which are used for low energy night vision ( the ultra and infra mean beyond visible spectrum)

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.