Roentgen discovered X-rays and Mosley found that the frequency of the X-rays emitted from anode increases with the
A. increase in the mass number of the metal used as anode
B. decrease in the mass number of the metal used as anode
C. decrease in the proton number of the metal used as anode
D. increase in the proton number of the metal used as anode
Correct Answer: D. increase in the proton number of the metal used as anode