Answer:
1. Effective nuclear charge (Zeff)
2. Less
3. Shield
Step-by-step explanation:
The effective nuclear charge (Zeff) is defined as the nuclear charge that is experienced by an electron of an atom having atomic number > 1.
The effective nuclear charge experienced by a given electron is always less than the actual nuclear charge of the nucleus of the atom. This is because of the shielding effect of the inner electrons of the atom.
The shielding effect is defined as the shielding of an electron from the positive nuclear charge of the nucleus by the inner electrons of an atom.
Therefore, the outer electrons of an polyelectronic atom are shielded by the inner electrons from the nuclear charge of the nucleus.