21. Which of the following d-block elements does not show variable oxidation states?
A) Zn
B) Fe
C) Ni
D) Co
Answer: A
Explanation:
Zinc (Zn) does not show variable oxidation states; it exhibits only a +2 oxidation state in its compounds because its dd-subshell is completely filled (3d¹⁰), and it cannot lose or gain more electrons to exhibit other oxidation states.
22. The shielding effect of 4f electrons in lanthanides is:
A) Very effective
B) Less effective than 5d electrons
C) More effective than 3d electrons
D) Poorly effective
Answer: D
Explanation:
The 4f electrons in lanthanides have a very poor shielding effect because they are more deeply buried within the atom, and the penetration of their electron cloud is less significant. This leads to an increase in the effective nuclear charge experienced by the outer electrons.
23. The most common oxidation state for actinides is:
A) +2
B) +3
C) +4
D) +5
Answer: B
Explanation:
The most common oxidation state for actinides is +3, similar to lanthanides. However, actinides also show a wide variety of oxidation states due to their ability to lose electrons from both 5f and 6d orbitals.
24. Transition metals form complexes due to:
A) Small size and high charge
B) Ability to donate electrons
C) Large atomic size
D) Inability to form bonds with ligands
Answer: A
Explanation:
Transition metals form complexes because they have a small size and high charge, which allows them to attract ligands (species that donate electron pairs) and form stable complexes. Their partially filled d-orbitals also play a crucial role in complex formation.
25. Which of the following statements is correct about the magnetic properties of transition metals?
A) All transition metals are diamagnetic
B) Transition metals have magnetic moments due to unpaired electrons
C) Transition metals do not have magnetic properties
D) Magnetic properties of transition metals are due to paired electrons
Answer: B
Explanation:
Transition metals exhibit magnetic properties due to the presence of unpaired electrons in their d-orbitals. These unpaired electrons generate a magnetic moment, leading to paramagnetism. The more unpaired electrons, the stronger the magnetic properties.
26. Which of the following ions is likely to be colorless in solution?
A) Fe2+
B) Cu2+
C) Zn2+
D) Ni2+
Answer: C
Explanation:
The Zn2+ ion is colorless in solution because it has a completely filled d-subshell (3d¹⁰). Since there are no unpaired electrons, d-d transitions that would result in color cannot occur, making it colorless.
27. The ability of transition metals to form complexes is due to:
A) Their large atomic size
B) Their tendency to lose electrons easily
C) The presence of vacant d-orbitals
D) Their high electropositivity
Answer: C
Explanation:
Transition metals have vacant d-orbitals that can accept electron pairs from ligands to form coordination complexes. This ability to form complexes is one of the characteristic properties of transition metals.
28. The actinides show a greater range of oxidation states compared to lanthanides because:
A) Their 5f orbitals are more diffused
B) They have more valence electrons
C) They form stronger bonds with ligands
D) Their atomic radii are smaller
Answer: A
Explanation:
The 5f orbitals in actinides are more diffused compared to the 4f orbitals in lanthanides. This allows actinides to have a greater range of oxidation states, as electrons from both the 5f and 6d orbitals can participate in bonding.
29. Which of the following elements is not part of the first transition series?
A) Scandium
B) Chromium
C) Copper
D) Palladium
Answer: D
Explanation:
Palladium (Pd) is part of the second transition series, not the first. The first transition series includes elements from Scandium (Z = 21) to Copper (Z = 29), while Palladium belongs to the series starting from Yttrium (Z = 39).
30. Which of the following oxides is amphoteric?
A) Cr2O3
B) Mn2O7
C) ZnO
D) Fe2O3
Answer: A
Explanation:
Cr2O3Cr2O3 (chromium(III) oxide) is an amphoteric oxide, meaning it can react with both acids and bases. Amphoteric oxides can behave as both acidic and basic oxides depending on the reaction environment.
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