J.J Thomson was the one who discovered the electron so your answer is 5. or E
Answer:- 
Solution:- Wavelength is given and we are asked to calculate the frequency. The equation that correlates frequency with wavelength is:

where,
is the symbol for frequency, c is the symbol for speed of light and
is the symbol for wavelength.
Speed of light is
and the wavelength is given as
.
Let's plug in the values in the equation and so the calculations to calculate the frequency:


(since,
)
So, the frequency of the wave is
.