1. An element is placed in the \(d\)-block when its differentiating electron enters mainly the:
ⓐ. outer \(np\) subshell
ⓑ. penultimate \((n-1)d\) subshell
ⓒ. outer \(ns\) subshell
ⓓ. antepenultimate \((n-2)f\) subshell
Correct Answer: penultimate \((n-1)d\) subshell
Explanation: The \(d\)-block is identified by the progressive entry of differentiating electrons into a \(d\) subshell of the penultimate shell. Its characteristic subshell is written as \((n-1)d\), while the outer shell may also contain \(ns\) electrons. Entry into \(ns\), \(np\), and \((n-2)f\) instead characterises the \(s\)-, \(p\)-, and \(f\)-blocks, respectively. The word “block” therefore refers to the subshell being filled across a sequence of elements. This placement idea is broader than the later, more restrictive definition of a transition element.
2. The inner-transition series are associated primarily with progressive filling of the:
ⓐ. \(np\) subshell
ⓑ. \((n-2)f\) subshell
ⓒ. \(ns\) subshell
ⓓ. \((n-1)d\) subshell
Correct Answer: \((n-2)f\) subshell
Explanation: Inner-transition elements belong to the \(f\)-block, where the differentiating electron enters an \((n-2)f\) subshell. This subshell lies two principal shells below the outermost shell, which motivates the term “inner-transition.” The two \(f\)-block series are usually displayed separately below the main body of the periodic table to keep the table compact. Their detached display does not mean that they are chemically disconnected from periods \(6\) and \(7\). Confusing \((n-2)f\) with \((n-1)d\) would interchange the defining subshells of the \(f\)- and \(d\)-blocks.
3. Use the periodic-table arrangement described below: a left block is followed by a central block and then a right block, while two long rows are printed separately beneath the table. The most suitable identification is:
ⓐ. central block: \(d\)-block; detached rows: \(f\)-block
ⓑ. central block: \(p\)-block; detached rows: \(d\)-block
ⓒ. central block: \(s\)-block; detached rows: \(p\)-block
ⓓ. central block: \(f\)-block; detached rows: \(s\)-block
Correct Answer: central block: \(d\)-block; detached rows: \(f\)-block
Explanation: In the long form of the periodic table, the \(d\)-block occupies the central region between the \(s\)- and \(p\)-blocks. The \(f\)-block is conventionally shown as two separate rows below the main table. This layout prevents the table from becoming excessively wide while preserving the actual periodic sequence. The central placement of the \(d\)-block reflects the filling of \((n-1)d\) orbitals after the \(ns\) subshell begins to fill. The detached position is therefore a display choice, not a separate periodic system.
4. In the phrase “progressive filling of an inner subshell,” progressive filling means that:
ⓐ. every new element receives a completely filled subshell at once
ⓑ. electrons are removed successively from the same subshell across a series
ⓒ. successive elements generally add electrons to that subshell
ⓓ. all orbitals of the atom gain one electron simultaneously
Correct Answer: successive elements generally add electrons to that subshell
Explanation: Across a block, the differentiating electron is added successively to the subshell that characterises that block. In the \(d\)-block this is mainly \((n-1)d\), whereas in the \(f\)-block it is mainly \((n-2)f\). The subshell does not become full in a single step; its occupancy increases over a sequence of elements. Other subshells may also be occupied, and small energy differences can later produce configuration irregularities. The central idea is a gradual change in occupancy rather than simultaneous filling of every orbital.
5. The elements \(\mathrm{Fe}\), \(\mathrm{Cr}\), \(\mathrm{Ce}\), and \(\mathrm{U}\) are classified respectively as:
ⓐ. \(d\)-block, \(d\)-block, lanthanoid, actinoid
ⓑ. lanthanoid, \(d\)-block, actinoid, \(p\)-block
ⓒ. \(d\)-block, \(p\)-block, lanthanoid, actinoid
ⓓ. actinoid, lanthanoid, \(p\)-block, \(d\)-block
Correct Answer: \(d\)-block, \(d\)-block, lanthanoid, actinoid
Explanation: Iron and chromium are familiar members of the central \(d\)-block. Cerium belongs to the lanthanoid series, which is associated with progressive \(4f\) filling. Uranium belongs to the actinoid series, associated with \(5f\) filling. Lanthanoids and actinoids together form the two inner-transition series. The classification depends on periodic position and electronic structure rather than merely on metallic character.
6. For a \(d\) subshell, the azimuthal quantum number is ______.
ⓐ. \(0\)
ⓑ. \(3\)
ⓒ. \(1\)
ⓓ. \(2\)
Correct Answer: \(2\)
Explanation: The azimuthal quantum number \(l\) identifies the subshell type. The sequence is \(l=0\) for \(s\), \(l=1\) for \(p\), \(l=2\) for \(d\), and \(l=3\) for \(f\). Thus a \(d\) subshell is specified by \(l=2\). This value later determines that the subshell contains \(2l+1=5\) orbitals. The blank tests the symbolic connection between the subshell label and its quantum number rather than a verbal definition.
7. Match each quantum number in Column I with its principal role in Column II.
| Column I | Column II |
|---|
| P. \(n\) | 1. Orientation of an orbital within a subshell |
| Q. \(l\) | 2. Principal shell |
| R. \(m_l\) | 3. Spin orientation of an electron |
| S. \(m_s\) | 4. Subshell type |
ⓐ. P-4, Q-2, R-3, S-1
ⓑ. P-2, Q-1, R-4, S-3
ⓒ. P-2, Q-4, R-1, S-3
ⓓ. P-1, Q-4, R-2, S-3
Correct Answer: P-2, Q-4, R-1, S-3
Explanation: The principal quantum number \(n\) identifies the main shell, so P matches \(2\). The azimuthal quantum number \(l\) identifies the subshell type, so Q matches \(4\). The magnetic quantum number \(m_l\) distinguishes orbital orientations within a subshell, giving R-\(1\). The spin quantum number \(m_s\) describes the two allowed spin orientations of an electron, giving S-\(3\). Keeping these roles separate prevents confusion between an orbital’s orientation and an electron’s spin.
8. A subshell has \(l=2\). Using the relations \(2l+1\) orbitals per subshell and a maximum of \(2\) electrons per orbital, its orbital count and maximum electron capacity are:
ⓐ. \(5\) orbitals and \(10\) electrons
ⓑ. \(3\) orbitals and \(6\) electrons
ⓒ. \(7\) orbitals and \(14\) electrons
ⓓ. \(5\) orbitals and \(5\) electrons
Correct Answer: \(5\) orbitals and \(10\) electrons
Explanation: \( \textbf{Known value:} \) The subshell has \(l=2\).
\( \textbf{Identify the subshell:} \) The value \(l=2\) corresponds to a \(d\) subshell.
\( \textbf{Orbital-count relation:} \)
\[
\text{Number of orbitals}=2l+1
\]
\( \textbf{Substitute the value of } l\textbf{:} \)
\[
2(2)+1=5
\]
\( \textbf{Electron limit per orbital:} \) Each orbital can contain at most \(2\) electrons with opposite spins.
\( \textbf{Maximum subshell capacity:} \)
\[
5\times2=10\text{ electrons}
\]
\( \textbf{Final answer:} \) The subshell contains \(5\) orbitals and can accommodate at most \(10\) electrons. Counting one electron per orbital would describe a half-filled \(d\) subshell, not its maximum capacity.
9. Which pair gives the orbital count and maximum electron capacity of an \(f\) subshell?
ⓐ. \(5\) orbitals and \(10\) electrons
ⓑ. \(7\) orbitals and \(14\) electrons
ⓒ. \(3\) orbitals and \(6\) electrons
ⓓ. \(7\) orbitals and \(7\) electrons
Correct Answer: \(7\) orbitals and \(14\) electrons
Explanation: For an \(f\) subshell, \(l=3\), so the number of orbitals is \(2l+1=7\). Each orbital can hold a maximum of \(2\) electrons with opposite spins. The total capacity is therefore \(7\times2=14\) electrons. A set of \(7\) singly occupied orbitals represents a half-filled \(f^7\) arrangement, not a completely filled subshell. The pair \(5\) orbitals and \(10\) electrons belongs to a \(d\) subshell.
10. Three electrons are to be placed in five degenerate \(d\) orbitals. The ground-state arrangement that follows Hund’s rule is:
ⓐ. \([\uparrow][\uparrow][\uparrow][\,][\,]\)
ⓑ. \([\uparrow\downarrow][\uparrow][\,][\,][\,]\)
ⓒ. \([\uparrow][\downarrow][\uparrow][\,][\,]\)
ⓓ. \([\uparrow\downarrow\uparrow][\,][\,][\,][\,]\)
Correct Answer: \([\uparrow][\uparrow][\uparrow][\,][\,]\)
Explanation: Hund’s rule states that electrons occupy degenerate orbitals singly before any pairing begins. The singly occupied orbitals also have parallel spins in the lowest-energy arrangement. For \(3\) electrons in five \(d\) orbitals, three separate orbitals are therefore occupied by one electron each. Option B pairs electrons while vacant orbitals remain, whereas option C does not keep the three single electrons parallel. Option D places \(3\) electrons in one orbital and violates the two-electron limit imposed by the Pauli principle.
11. The Pauli exclusion principle places the following restriction on a single orbital:
ⓐ. it may contain any number of electrons if their energies differ
ⓑ. it may contain only one electron under all circumstances
ⓒ. it may contain at most two electrons with opposite spins
ⓓ. it may contain two electrons with parallel spins
Correct Answer: it may contain at most two electrons with opposite spins
Explanation: An orbital is specified by a particular set of \(n\), \(l\), and \(m_l\) values. Two electrons may occupy that same orbital only if their spin quantum numbers are opposite, \(m_s=+\frac{1}{2}\) and \(m_s=-\frac{1}{2}\). This gives a maximum of \(2\) electrons per orbital. Parallel-spin electrons must occupy different orbitals when such orbitals are available. Pauli’s principle therefore sets the capacity of each orbital, while Hund’s rule controls how electrons spread among degenerate orbitals before pairing.
12. The qualitative stability of half-filled and completely filled subshells is best interpreted by the statement:
ⓐ. every \(d^4\) atom must change to \(d^5\), regardless of the energy required
ⓑ. such stability matters when nearby orbital energies are close
ⓒ. paired electrons can never occur in a \(d\) or \(f\) subshell
ⓓ. a completely filled \(d^{10}\) subshell can never lose an electron
Correct Answer: such stability matters when nearby orbital energies are close
Explanation: Half-filled and completely filled subshells can receive extra stabilisation from favourable electron distribution and exchange effects. This influence becomes especially relevant when nearby subshells have very similar energies. It does not mean that every atom must rearrange to obtain \(d^5\) or \(d^{10}\), because the total energy balance still matters. Pairing remains possible and is necessary as a subshell moves beyond half-filled occupancy. The idea is therefore a qualitative contributor to certain configuration exceptions, not an absolute rule that overrides all other energetic factors.
13. Use the arrangement of transition series given below.
P. First transition series
Q. Second transition series
R. Third transition series
S. Fourth transition series
The appropriate sequence of characteristic subshells is:
ⓐ. P-\(3d\), Q-\(5d\), R-\(4d\), S-\(6d\)
ⓑ. P-\(4d\), Q-\(3d\), R-\(6d\), S-\(5d\)
ⓒ. P-\(3d\), Q-\(4d\), R-\(5d\), S-\(6d\)
ⓓ. P-\(4d\), Q-\(5d\), R-\(6d\), S-\(7d\)
Correct Answer: P-\(3d\), Q-\(4d\), R-\(5d\), S-\(6d\)
Explanation: The first transition series involves progressive filling of the \(3d\) subshell. The second and third transition series similarly involve \(4d\) and \(5d\) filling, respectively. The fourth transition series is associated with the incomplete \(6d\) series. The principal quantum number of the occupied \(d\) subshell increases by one from one transition series to the next. Reversing \(3d\) and \(4d\) would also reverse the period assignments of the first two series.
14. Consider the following statements about the transition series.
Statement I: The \(3d\) series occurs in period \(4\).
Statement II: The \(4d\) series occurs in period \(5\).
Statement III: The \(5d\) series occurs in period \(6\).
Statement IV: The \(6d\) series belongs to period \(7\) and is incomplete.
The valid statements are:
ⓐ. I and II only
ⓑ. II, III and IV only
ⓒ. I, II and III only
ⓓ. I, II, III and IV
Correct Answer: I, II, III and IV
Explanation: In period \(4\), electrons enter the \(3d\) subshell after the \(4s\) subshell has begun filling. Periods \(5\) and \(6\) similarly contain the \(4d\) and \(5d\) transition series. The \(6d\) series belongs to period \(7\). It is described as incomplete because the sequence of known elements and their configurations does not provide a fully established series comparable with the earlier three. The period number is one greater than the principal quantum number of the characteristic \((n-1)d\) subshell.
15. For a transition-series element with the simplified valence configuration \((n-1)d^3ns^2\), the usual group-number relation places it in group:
ⓐ. \(3\)
ⓑ. \(7\)
ⓒ. \(12\)
ⓓ. \(5\)
Correct Answer: \(5\)
Explanation: \( \textbf{Configuration supplied:} \) The relevant electrons are \((n-1)d^3ns^2\).
\( \textbf{Electrons counted for the group:} \) In this part of the \(d\)-block, the \((n-1)d\) and \(ns\) electrons are counted together.
\( \textbf{Number of } d\textbf{ electrons:} \)
\[
3
\]
\( \textbf{Number of } s\textbf{ electrons:} \)
\[
2
\]
\( \textbf{Group-number inference:} \)
\[
3+2=5
\]
\( \textbf{Periodic interpretation:} \) The configuration therefore corresponds to group \(5\).
\( \textbf{Final answer:} \) The element is placed in group \(5\). Counting only the \(ns\) electrons would ignore the characteristic contribution of the \((n-1)d\) subshell.
16. A period-\(6\) element lies in the central block after the separately represented lanthanoid sequence. Its differentiating electron is entering a \(d\) subshell. The element belongs to the:
ⓐ. \(5d\) transition series
ⓑ. \(4d\) transition series
ⓒ. \(6d\) transition series
ⓓ. \(4f\) inner-transition series
Correct Answer: \(5d\) transition series
Explanation: The central \(d\)-block portion of period \(6\) is associated with progressive filling of the \(5d\) subshell. The \(4f\) subshell is filled through the lanthanoid sequence, which is displayed separately below the main table. After this inner filling, the period continues into the \(5d\) series. The \(4d\) series belongs to period \(5\), while \(6d\) belongs to period \(7\). The detached placement of the lanthanoids can obscure this continuous period-\(6\) order.
17. An element is classified operationally as a transition element when it has:
ⓐ. a completely filled \(d\) subshell in both its atom and all common ions
ⓑ. any metallic atom located outside the \(p\)-block
ⓒ. at least one electron in its outermost shell
ⓓ. a partially filled \(d\) subshell in its atom or a common ion
Correct Answer: a partially filled \(d\) subshell in its atom or a common ion
Explanation: The operational definition focuses on the occupancy of the \(d\) subshell. An element qualifies when its atom has an incomplete \(d\) subshell or when at least one of its common ions has an incomplete \(d\) subshell. The definition therefore includes evidence from common oxidation states, not only from the neutral atom. Metallic character and central periodic-table location are not by themselves sufficient. A completely filled \(d^{10}\) arrangement in both the atom and common ions fails the defining electronic requirement.
18. Three hypothetical elements have the configurations shown below.
| Element | Neutral atom | Common ion |
|---|
| P | \((n-1)d^{10}ns^2\) | \(\mathrm{P^{2+}}:(n-1)d^{10}\) |
| Q | \((n-1)d^{10}ns^1\) | \(\mathrm{Q^{2+}}:(n-1)d^9\) |
| R | \((n-1)d^0ns^2\) | \(\mathrm{R^{2+}}:(n-1)d^0\) |
On the basis of the operational definition, the transition element is:
ⓐ. P only
ⓑ. R only
ⓒ. Q only
ⓓ. P and R only
Correct Answer: Q only
Explanation: Element Q has a common \(+2\) ion with configuration \((n-1)d^9\), so its \(d\) subshell is partially filled in a common oxidation state. Element P has \(d^{10}\) in both the atom and the common \(+2\) ion, so no incomplete \(d\) subshell appears in the supplied chemistry. Element R has \(d^0\) in both cases, which is empty rather than partially filled. The neutral configuration of Q is \(d^{10}\), but the common-ion condition still allows it to qualify. Classification must examine all relevant configurations supplied, not just the neutral atom.
19. Examine the following statements.
Statement I: Every transition element belongs to the \(d\)-block.
Statement II: Every \(d\)-block element must necessarily be a transition element.
Statement III: A common ion with a partially filled \(d\) subshell can establish transition character even when the neutral atom has \(d^{10}\).
The valid statements are:
ⓐ. I and II only
ⓑ. I and III only
ⓒ. II and III only
ⓓ. I, II and III
Correct Answer: I and III only
Explanation: Transition elements are drawn from the \(d\)-block because their defining incomplete subshell is a \(d\) subshell. The reverse statement is not universally valid, since some \(d\)-block elements have \(d^{10}\) configurations in both their atoms and common ions. A neutral \(d^{10}\) configuration does not automatically exclude an element if a common ion has \(d^1\) to \(d^9\) occupancy. Statement III captures this atom-or-common-ion condition. The relationship is therefore one-way unless the electronic configurations are checked.
20. Match the electronic situation in Column I with the description in Column II.
| Column I | Column II |
|---|
| P. Atom has \(d^3\) | 1. Transition character established by the atom |
| Q. Atom and common ion both have \(d^{10}\) | 2. Transition character established by a common ion |
| R. Atom has \(d^{10}\), but a common ion has \(d^8\) | 3. No transition character from the supplied configurations |
| S. Atom and common ion both have \(d^0\) | 4. No partially filled \(d\) subshell in either supplied state |
The appropriate matching is:
ⓐ. P-2, Q-1, R-3, S-4
ⓑ. P-1, Q-4, R-3, S-2
ⓒ. P-3, Q-2, R-1, S-4
ⓓ. P-1, Q-3, R-2, S-4
Correct Answer: P-1, Q-3, R-2, S-4
Explanation: An atom with \(d^3\) already has a partially filled \(d\) subshell, so P matches \(1\). If both the atom and its common ion are \(d^{10}\), the supplied configurations show no transition character, giving Q-\(3\). For R, the common \(d^8\) ion establishes transition character even though the neutral atom is \(d^{10}\), so R matches \(2\). A \(d^0\) subshell is empty rather than partially filled, making S-\(4\). Both \(d^0\) and \(d^{10}\) lie outside the incomplete range \(d^1\) to \(d^9\).
