Which of the following best helps to explain why the atomic radius of K is greater than that of Br? A) The first ionization energy of K is higher than that of Br.
B) The valence electrons in K are in a higher principal energy level than those of Br.
C) In the ground state, an atom of K has fewer unpaired electrons than an atom of Br has.
D) The effective nuclear charge experienced by valence electrons is smaller for K than for Br.