Question

compute the ionization energy for a single atom of hydrogen

Answer 1

Look up the first ionization energy for hydrogen. It should be about 131 kJ/mol. Determine the number of hydrogen atoms in one mole. This should be straightforward, if you think about it carefully. Now, if you know the ionization energy for a mole of hydrogen, and you know how many atoms are in one mole of hydrogen, figure out how you would get the ionization energy for one hydrogen atom.