Start by getting the symbol of the element right. It's Mo. And Mo has six valence electrons. You can tell because it is in group VIB on the periodic table. The Roman numeral tells the number of valence electrons.

No. The MASS NUMBER is the sum of the protons and neutrons. The mass number is ALWAYS a whole number. The atomic mass is the weighted average mass of all of the naturally occurring isotopes of the element. To get the number of neutrons in an isotope you subtract the atomic number for that element from the mass number of the isotope.

For instance, consider U-235. 235 is the mass number of the fissionable isotope of uranium. Subtract 92 from 235 to get the number of neutrons in an atom of U-235.

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