Answer:
50 MHz
Explanation:
The relation between frequency and wavelength is shown below as:

c is the speed of light having value 
Given, Wavelength = 6 m
Thus, Frequency is:



Also,
Also, 1 Hz =
MHz
So,<u> Frequency = 50 MHz.</u>
B
Explanation:
option b is correct because
hydrogen is smallest atom
isotopes of elements have different atomic mass
atom mass have nothing to do with elemental identity