Question 3
Why are ionization energies given for a mole of atoms rather than for one atom?
The right answer is the one marked above.
Because for a single atom this energy is a very small quantity. So the value is quoted for 6.022 × 1023 atoms — one mole — and the unit is kJ mol−1.
The energy per atom does not change with how many atoms you have; a mole is simply a convenient number to scale up to, so that the figures come out in units a person can read and compare.