NEET Chemistry: d- and f-Block Elements questions with solutions

Q1. The stability of ferric ion is due to

1. half filled f-orbitals
2. half filled d-orbitals
3. completely filled f-orbitals
4. completely filled d-orbitals

Answer: half filled d-orbitals

Ferric ion is Fe3+, which has the configuration [Ar] 3d5. A half-filled d-subshell is especially stable because it has maximum exchange energy and symmetrical distribution of electrons.

Q2. Which out of the following belongs to \( 3 d \) -series? This question has multiple correct options

1. copper
2. cobalt
3. gold
4. silver

Answer: cobalt

Cobalt is a first-row transition element with electron configuration [Ar] 3d^7 4s^2, so it belongs to the 3d series. Copper, silver, and gold are in the 4d/5d series, not the 3d series.

Q3. Why d-block element form complexes?

1. due to larger size and higher nuclear charge
2. due to small size and low nuclear charge
3. due to small size and higher nuclear charge
4. none of the above

Answer: due to small size and higher nuclear charge

d-block ions often have relatively small ionic radii and high effective nuclear charge, giving them high charge density. This makes them strong Lewis acids, so they readily accept lone pairs from ligands and form complexes.