General Chemistry

Step 1: Werner’s coordination theory.
According to Werner’s theory, metals exhibit two types of valences: primary and secondary valence. These explain the bonding behavior in coordination compounds.

Step 2: Meaning of primary valence.
Primary valence corresponds to the oxidation state of the metal and is satisfied by ions. It is ionisable in nature.

Step 3: Relation with ionisable valence.
Since primary valence can be ionised in solution, it is also called ionisable valence.

Step 4: Conclusion.
Thus, primary valence is correctly referred to as ionisable valence.

Step 1: Understanding contraction effect.
Both lanthanoid and actinoid series show contraction due to poor shielding effect of -electrons, leading to a gradual decrease in atomic and ionic radii.

Step 2: Comparison of shielding.
In actinoids, the -electrons have even poorer shielding compared to -electrons of lanthanoids. Additionally, relativistic effects are more prominent in actinoids.

Step 3: Analysis of given statements.
Lanthanoids form fewer complexes than actinoids, actinoid hydroxides are generally more basic, and -orbitals are more deeply buried (higher binding energy) than -orbitals.

Step 4: Conclusion.
Hence, the correct statement is (B) Actinoid contraction is greater than lanthanoid contraction.