Comprehension Type
Direction (Q. Nos. 16 and 17) This section contains a paragraph, describing theory, experiments, data, etc. Two questions related to the paragraph have been given. Each question has only one correct answer among the four given options (a), (b), (c) and (d).
Passage
The observed oxidation state of lanthanides either in solution or in insoluble compounds form tripositive cations. Based on the ionisation enthalpies and hydration energy factors, it is concluded that tripositive species is more stable than di or tetrapositive species in aqueous solution. In general, ions having half-filled (Tb4+ , Eu2+ , Gd3+) or completely filled 4f orbitals (Yb2+, Lu3+) or noble gas configuration (La3+, Ce4+) are stable. This is supported by their SRP values. Ions with + 4 oxidation state act as oxidising and ions having + 2 oxidation state act as reducing agents. Ions having same number of unpaired electrons in f-orbitals possess same colour.
Q.
Observe the following equations.
Sm3+(aq) + e- → Sm2+ (aq), E° = - 1.55 V
Eu3+(aq) + e- → Eu2+ (aq), E° = - 0.43 V
Yb3+(aq) + e- → Yb2+ (aq), E° = - 1.55V
Based on the above equations, the correct reducing strength is in the order of