The periodicity of the properties of elements is chiefly due to the

i) numbers of electrons in the atoms of the elements

ii) distribution of electrons in the atoms of the elements

iii) numbers of neutrons in the atoms of the elements

a) i only

b) i and iii only

c) all of these

d) ii only

e) iii only

f) ii and iii only

g) none of these

h) i and ii only