Across a Row in the Periodic Table, the Ionization Energy $\ell$

Across a row in the periodic table, the ionization energy ________

A) increases because the n quantum number changes.
B) increases because the $\ell$ quantum number changes.
C) decreases because the effective nuclear charge decreases.
D) increases because the effective nuclear charge increases.
E) changes little because the outer electrons all are in the same shell.