11. Transition metals form colored compounds because:
A) They absorb light and re-emit it
B) d-d transitions of electrons
C) f-f transitions of electrons
D) They have paired electrons
Answer: B
Explanation:
Transition metals form colored compounds due to d-d transitions. When light is absorbed, electrons jump from a lower energy d-orbital to a higher energy one (d-d transition). The color observed is due to the wavelength of light that is not absorbed, which is the complementary color of the absorbed light.
12. Which of the following is not an f-block element?
A) Cerium
B) Thorium
C) Neodymium
D) Zinc
Answer: D
Explanation:
Zinc is not an f-block element; it belongs to the d-block. The f-block elements are lanthanides and actinides, where electrons are filling the 4f or 5f orbitals.
13. The element with atomic number 57 belongs to which block of the periodic table?
A) s-block
B) p-block
C) d-block
D) f-block
Answer: D
Explanation:
The element with atomic number 57 is lanthanum (La), and it is the first element of the f-block, specifically starting the lanthanide series. Lanthanum itself, however, is often placed in the d-block but marks the beginning of the f-block.
14. Which of the following ions is colorless in aqueous solution?
A) Cu2+
B) Fe3+
C) Zn2+
D) Co2+
Answer: C
Explanation:
Zn2+ is colorless in aqueous solution because it has a completely filled d-subshell (3d¹⁰). Since there are no unpaired d-electrons, it cannot undergo d-d transitions, which are responsible for color in transition metal ions.
15. Which of the following compounds will exhibit the strongest magnetic properties?
A) [Ti(H2O)6]3+
B) [Cu(NH3)4]2+
C) [Fe(CN)6]4−
D) [MnO4]−
Answer: D
Explanation:
[MnO4]− (permanganate ion) contains manganese in the +7 oxidation state. Although this particular ion does not exhibit strong magnetic properties because there are no unpaired electrons in Mn⁷⁺, the magnetic properties depend on the specific electronic configuration. Among the options, [Ti(H2O)6]3+ has the most unpaired electrons, thus exhibiting stronger paramagnetism.
16. The f-block elements are also known as:
A) Transition metals
B) Inner transition metals
C) Heavy metals
D) Alkali metals
Answer: B
Explanation:
The f-block elements are referred to as “inner transition metals” because their f-orbitals are progressively filled as you move across the period, and they are located separately from the main body of the periodic table.
17. The first transition series includes elements from:
A) Scandium to Copper
B) Titanium to Zinc
C) Vanadium to Manganese
D) Chromium to Nickel
Answer: A
Explanation:
The first transition series includes the elements from scandium (Z = 21) to copper (Z = 29). These elements have partially filled 3d orbitals and exhibit typical properties of transition metals such as variable oxidation states and the formation of colored compounds.
18. Which of the following lanthanide ions is colorless?
A) Ce4+
B) Eu3+
C) Tb3+
D) Pr3+
Answer: A
Explanation:
Ce4+Ce4+ is colorless because it has no f-electrons. In its +4 oxidation state, cerium has an empty 4f subshell, and therefore, it cannot undergo f-f transitions, which are responsible for the color of lanthanide ions.
19. Which of the following is an alloy of copper and zinc?
A) Brass
B) Bronze
C) Steel
D) Nichrome
Answer: A
Explanation:
Brass is an alloy of copper and zinc. It is commonly used in applications requiring corrosion resistance and malleability.
20. The stability of the +3 oxidation state decreases in the sequence:
A) Sc>Ti>V>Cr>Mn
B) Mn>Cr>V>Ti>Sc
C) V>Cr>Mn>Ti>Sc
D) Sc>V>Mn>Cr>Ti
Answer: A
Explanation:
The stability of the +3 oxidation state decreases in the sequence Sc>Ti>V>Cr>. As we move across the 3d series, the energy required to remove electrons from the d-orbitals increases, and higher oxidation states become less stable compared to lower ones.
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