What factor(s) may be responsible for the ionization energy within a period?

a.) the valence electrons are further from the nucleus when moving from left to right.
b.) the valence electrons remain at the same distance from the nucleus when moving left to right.
c.) the diameter of the atom decreases somewhat as electrons are added.
d.) the attractive force of the nucleus increases.

"The diameter of the atom decreases somewhat as electrons are added" and "The attractive force of the nucleus increases" are the factors that may be responsible for the ionization energy within a period. The correct options among all the options that are given in the question are option "C" and option "D".

The factors  that may  be  responsible  for  the ionization energy  within  a period  is

The diameter  of the atom decreases  somewhat as electrons are  added.The attractive force of the nucleus increases

   Explanation

ionization  energy  is the Electron  shielding. Generally  there  is  increase of  ionization  across the period  that is from the left  to the right.Across  the period ( from left  to right)  the diameter   of the atom  decreases. This make it harder  to remove  an electron as you go across the period,  thus ionization energy increase across the period (  from left  to right).The force of attraction of the  nucleus increase across the period ( from left to right). This is due to increase in number of protons across the period.