a.
When the effective nuclear charge felt by the valence electrons is low
b.
When the effective nuclear charge felt by the valence electron is high
c.
When the valence electrons are close to the nucleus
d.
When the valence electron is at the zeroth order
a. When the effective nuclear charge felt by the valence electrons is low, the electron will be less tightly held by the nucleus and more easily ionized or involved in chemical reactions.
b. When the effective nuclear charge felt by the valence electron is high, the electron will be more tightly held by the nucleus and less likely to be involved in chemical reactions.
c. When the valence electrons are close to the nucleus, they will feel a stronger effective nuclear charge and be more tightly held by the nucleus.
d. When the valence electron is at the zeroth order, it is in the outermost energy level and determines the chemical properties of the atom.