The elements in group 2 are known as the alkaline earth metals. As you move down the group of the periodic table, additional shells of electrons are added that increase the atomic radius.

As the atomic radius decreases, the nucleus has a tighter hold on its electrons, so more energy is required to remove them. Therefore, the ionisation energy of alkaline earth metals decreases going down a group.

Melting point decreases going down group 2 of the periodic table as metallic bonds are weaker for larger elements and less energy is required to break them. Magnesium is an exception, with an unusually low melting point.

The melting point of alkaline earth metals decreases going down the group. Thus, the element that is in the lowest position of group 2 in the periodic table would have the lowest melting point, that is, barium.

barium

As the atomic radius decreases, the nucleus has a tighter hold on its electrons, so more energy is required to remove them. Therefore, the ionisation energy of alkaline earth metals decreases going down a group and alkaline earth metal that has the lowest ionisation energy out of the elements provided is strontium.

strontium

As you go down a group, the atomic radius of atoms gets bigger as they gain additional shells of electrons.

additional shells of electrons

As the atomic radius decreases, the nucleus has a tighter hold on its electrons, so more energy is required to remove them. Therefore, the ionisation energy of alkaline earth metals decreases going down a group and alkaline earth metal that has the largest ionisation energy is beryllium.

beryllium

The atomic radius of alkaline earth metals increases going down the group of the periodic table. Thus, the alkaline earth metal that has the largest atomic radius is radium.

radium