Which of the following trends decrease down group 1 from Li → Cs? I. melting point
II. jonization energy
III. atomic radius
A.
I and II only
B.
II and III
C.
II and IIl only

D.
I and III only

A.  I and II only

Explanation:

As we move down the group atomic radii increased with increase of atomic number. The addition of electron in next level cause the atomic radii to increased. The hold of nucleus on valance shell become weaker because of shielding of electrons thus size of atom increased.

As the size of atom increases the ionization energy from top to bottom also  decreases because it becomes easier to remove the electron because of less nuclear attraction and as more electrons are added the outer electrons becomes more shielded and away from nucleus.

Melting point also goes to decreases because there is large distance between the positive nucleus and bonded electrons thus overall attraction goes to reduced and less energy is required to melt.