Answer: C. He measured the different wavelengths emitted by the electrons of the element using x-rays
Explanation: Moseley was the scientist who determined that atomic number of the element that is number of electrons in atoms of the particular elements.
He studied the X ray spectra of the atoms starting from aluminum and ending at gold. Out of the lines of the spectra, he determined the frequency of the particular line which was found to be increasing as the atomic mass of the element is increasing.
Then he explained that the frequency value of the line is precisely same as the serial number of element . Thus he specified Z as the atomic number symbol.
He also plotted the graph between the square root of the frequency and the atomic number which was found to be the straight line.
