Of elements in the same group those at the bottom of the periodic table have low ionization energies because of what?
(can be multiple answers)

a. layers of electron shells shield the protons attractive force
b. their atomic radius is larger
c. they have fewer electron shells to shield the protons from the electrons
d. these elements are high in electronegativity

Explanation:

When an electron is removed from a gaseous atom or ion then the energy required to do so is known as ionization energy.

When we move down a group then there is increase in mass of elements. This is due to increase in the number of electrons in an atom which increase the number of shells also.

Hence, these layers of electron shells will shield the nucleus of the atom. As a result, it would be easy to remove an electron from the outermost shell. Because of this less energy is needed to remove an electron hence, larger is the atomic radius of an atom lower will be its ionization energy.

Thus, we can conclude that of elements in the same group those at the bottom of the periodic table have low ionization energies because of following.

ammonium chloride & tallow

that would be because of both gravity and friction. so     c