Question

Answer the following question.
Statement-1: Shielding effect increases as we go down the group.
Statement-2: With an increase in the number of electrons in the penultimate shell, shielding effect increases.
A. Statement 1 is True: Statement 2 is True; Statement 2 is a correct explanation for statement 1
B.Statement 1 is true, Statement 2 is true;2 Statement 2 not a correct explanation for statement 1
C.Statement 1 is true, statement 2 is false
D.Statement 1 is false, statement 2 is true

Answer 1

There are different orbitals in an atom with different energies, the orbitals with the same energy are called degenerate orbitals. In a multielectron system the mutual repulsions between the electrons is the reason for different energies in a subshell.

Step by step answer: Let us understand the shielding effect to answer the above question correctly. We know that in a multi electron system stability of an atom is because total attractive interactions are more than the repulsive attractions. The attractive interactions in an electron increases with an increase in positive charge(${Z_e}$) on the nucleus due to the presence of electrons in the inner shell the electrons in the outer shell experience the full positive charge of the nucleus().
The effect will be lowered due to the partial screening of positive charge on the nucleus by the inner shell electrons. This is known as the shielding of the outer shell electrons from the nucleus by the inner shell electrons, and the net positive charge experienced by the outer electrons is known as effective nuclear charge (${Z_{eff}}$e).
Despite the shielding of the outer electrons from the nucleus by the inner shell electrons, the attractive force experienced by the outer shell electrons increases with increase of nuclear charge. In other words the energy of interaction between the nucleus and electrons( that is the orbital energy) decreases (that is more negative) with the increase of atomic number Z.
We know that atomic number decreases down the group and the penultimate shell is the last shell, hence it is farthest from the nucleus causing effective shielding. Adding more electrons completes the shell which also shields effectively.

Hence the correct option is A.

Note: The lower the value of (n+l) for an orbital, the lower is its energy. If two orbitals have the same value of( n+l), the orbital with the lower value of n will have lower energy. Lastly it may be mentioned that energies of the orbital in the same subshell decrease with the increase in the atomic number(${Z_{eff}}$ ).