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Question Bank Case
Class XII (Chemistry)
Unit: 10. d & f Block Elements
Source Based Question
Q.No.
Passage
1.
Questions
Read the passage given below and answer the following questions given below:
The f-block elements are those in which the differentiating electrons enters the (n-2)f
orbital. There are two series of f-Block elements corresponding to filling of 4f and 5forbitals. The series of 4f-orbitals is called lanthanoids. Lanthanoids show different
oxidation states depending upon stability of f0, f7 and f14 configurations, though the
most common oxidation state is +3. There is a regular decrease in the size of
lanthanoids ions with increase in atomic number which is known as lanthanoid
contraction.
1
The atomic number of three lanthanoid elements X, Y and Z are 65, 68 and 70
respectively, their Ln3+ electronic configuration is
A. 4f8, 4f11, 4f13
B. 4f11, 4f8, 4f13
C. 4f0, 4f2, 4f11
D. 4f3, 4f7, 4f9
2
lanthanoid contraction is observed in
A. Gd
B. At
C. Xe
D. Te
3
Name a member of the lanthanoid series which is well known to exhibit +4 oxidation
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state.
A. Cerium (X=58)
B. Europium (Z=63)
C. Lanthanum (Z=57)
D. Gadolinium (Z=64)
4
Identify the incorrect statement among the following.
A. Lanthanoid contraction is the accumulation of successive shrinkages.
B. The different radii of Zr and Hf due to consequences of the lanthanoid
contraction.
C. Shielding power of 4f electrons is quite weak.
D. There is a decrease in the radii of the atoms or ions proceeds from La to Lu
5
Which of the following is not the configuration of lanthanoid?
(A) [Xe]4f106s2
(B) [Xe]4f15d16s2
(C) [Xe]4f145d106s2
(D) [Xe]4f75d16s2
Answer
Q.No
Answer
1
A
2
A
3
A
4
B
5
C
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Q.No.
Questions
Passage
In Modern Periodic table, transition metals are placed in d-block. The general
2
electronic configuration of these elements is
(n – 1) d 1 – 10ns 1 – 2.
The d-orbitals of the penultimate energy level in their atoms receive electrons giving
rise to the three rows of the transition metals i.e., 3d, 4d and5d series. However, Zn,
Cd and Hg are not regarded as transition elements. Transition elements exhibit certain
characteristic properties like variable oxidation states, complex formation, formation
of coloured ions, alloys, catalytic activity etc. They are hard and have a high melting
point.
1
Which pair of transition metals of 3d series does not show variable oxidation state?
(a)
Scandium & Titanium
(c) Vanadium & Scandium
Answer
Passage
3
(b) Titanium & Vanadium
(d) Scandium & Zinc
1.(d)
Diamagnetic substances are those which are repelled by an applied
magnetic field. Such substances have no unpaired electron. Paramagnetic
substances are those which are attracted by an applied magnetic field.
Transition metals and many of their compounds show paramagnetic behavior
where there are unpaired electron or electrons. The magnetic moment arise
from the spin and orbital motions in ions or molecules. Magnetic moment of n
unpaired electrons is given as,
µ = √[n(n+2)] BohrMagneton. Magnetic moment increases as the number of
unpaired electrons increases.
1
In 3d series, the maximum magnetic moment is shown by–
(A) Sc(At. no. 21)
(B) V(At. No.23)
(C) Cr(At. No.24)
2
(D) Fe(At. No.26)
Which among the following ions has maximum value of magnetic moment–
(A) Cu2+
(B) Mn2+
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(C) Cr2+
3
4
5
Answer
(D) Ti2+
Increasing value of magnetic moments of
(I) [Fe(CN)6]4–
(II) [Fe(CN)6]3–
(III) [Cr(NH3)6]3+
(IV) [Ni(H2O)4]2+
(A) I < II < III < IV
(B) IV < III < II < I
(C) II < III < I < IV
(D) I < II < IV < III
Magnetic moment of [Ni(CN)4]2– is zero but that of [Ni(H2O)4]2+ is 2.83 B.M. It is
because of
(A)
CN– is a strong ligand making two unpaired electrons in Ni2+ to pair up,
while in [Ni(H2O)4]2+ two electrons remain unpaired as H2O is a weak ligand.
(B)
different oxidation state of Ni in two complexes.
(C)
both (A) and (B)
(D)
none of above
No. of unpaired electrons of Cr(Z = 24), Mn+ (Z = 25) and Fe2+ (Z = 26) are x, y
and z respectively. Which of the following order is correct–
(A) x < y < z
(B) x = y < z
(C) z < x = y
(D) x = y = z
1. [C]
2. [B]
3. [D]
4. [A]
5. [C]
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Passage
4
Most of the compounds of the transition metals are coloured in the solid or in
solution states. The colour of the transition metal ions arises from the excitation of
electrons from the d-orbitals of lower energy to the d-orbitals of higher energy. The
energy required for d-d electron excitation is available in the visible range.
Transition metal ions have the tendency to absorb certain radiations from the visible
region and exhibit the complementary colour.
The transition metal ions which have completely filled d-orbitals are colourless
as the excitation of electrons is not possible within d-orbitals. The transition metal
ions which have completely empty d-orbitals are also colourless. In certain oxysalts
of transition elements like KMnO4, K2Cr2O7, there are no unpaired electrons at the
central atom but they are deep in colour. The colour of these compounds is due to
charge transfer spectrum. For example, in MnO4–, an electron is transferred
momentarily from O2– to O– and manganese from Mn (+VII) to Mn(+ VI).
1
2
3
4
Select the correct statement –
(A) Colour of the transition metal ion arises due to d-d transition
(B) Colour of certain oxysalts of transition metals is due to charge transfer
(C) Both are correct
(D) None is correct
Which of the following is paramagnetic as well as coloured ion ?
(A) Cu+
(B) Cu2+
3+
(C) Sc
(D) Zn2+
Which is a coloured ion?
(A) [Cr(H2O)6]3+
(B) [Cu(CN)4]3–
(C) [Ti(H2O)6]4+
(D) [Sc(H2O)6]3+
K2Cr2O7 gives coloured solution in water. The colour is due to –
(A) d-d transition in Cr-atoms
(B) presence of unpaired electron in d-orbital in oxygen
(C) charge transfer from O to Cr
(D) none of the above
Answer
1. [C]
2. [B]
3. [A]
4.
[C]
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Passage
The elements of d-block which lie between the reactive metals of the s-block and the
5
elements of p-block are known as transition metal.
The transition elements were regarded as those elements which possessed
partially filled penultimate d-subshell in their ground state. Transition metals show
variable oxidation states except few. The most common oxidation state is +2. In
showing variable oxidation states, there are involvement of ns and unpaired electrons
of (n-1)d subshell. Lower states are ionic while higher states are covalent. Most of
transition metal and their compounds exhibit paramagnetism. Most of the compounds
of transition metals are coloured. The colour and paramagnetism are due to presence of
incomplete d-shell and unpaired electrons. They form there oxides on the surface.
The oxidation state of Mn atom in KMnO4 is…….
1
(a)
(b)
(c)
(d)
2
+3
+5
+7
+8
The spin only magnetic moment of Ni2+ in aqueous solution is------------(a) 0 BM
(b) 1.73 BM
(c) 2.84 BM
(d) 3.87 BM
3
Which element does not satisfy the definition of transition metals?
(a) Sc
(b) Cr
(c) Mn
(d) Zn
Answer:
1 (C)
2 (C)
3 (d)
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Passage
The f- block elements are those in which the differentiating electron enters the (n-2)f
6
orbital .There are two series of f-block elements corresponding to filling of 4f and 5forbitals called lanthanoids & actinoids respectively .They show different oxidation
states depending upon the stability of f0,f7&f14 configurations, though the principal
oxidation state is +3.There is a regular decrease in size of lanthanoid ions with increase
in atomic number & it is known as lanthanoid contraction. As a result of this, the basic
character of oxides and hydroxides decreases from first element(La) to last
element(Lu).All the actinoids are radioactive & therefore it is difficult to study their
chemical nature.
1
The atomic numbers of three lanthanoid elements X,Y&Z are 65,68&70 respectively.
The basic character of their hydroxides will decrease as (a)X>Y>Z
(b)X>Z>Y
(c)Z>Y>X
(d)Z>X>Y
2
Ce (Z=58)&Yb (Z=70) exhibit stable +4&+2 oxidation states respectively. This is
because(a)Ce4+&Yb2+ acquire f7 configurations.
(b)Ce4+&Yb2+ acquire f0 configurations.
(c)Ce4+&Yb2+ acquire f0&f14 configurations.
(d)Ce4+&Yb2+ acquire f7 & f14 configurations
Answer
1(a)
2(c)
Passage
7
The d-block of the periodic table contains the elements of the groups 3 to 12 and
are known as transition elements. In general, the electronic configuration of these
elements is (n – 1) d1 – 10 ns1 – 2 . The d-orbitals of the penultimate energy level in their
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atoms receive electrons giving rise to the three rows of the transition metals i.e., 3d, 4d
and5d series. However, Zn, Cd and Hg are not regarded as transition elements.
Transition elements exhibit certain characteristic properties like variable oxidation
stables, complex formation, formation of coloured ions, alloys, catalytic activity etc.
Transition metals are hard (except Zn, Cd and Hg) and have a high melting point.
1
2
3
4
Answer
Which transition metal of 3d series does not show variable oxidation state?
a. Sc
b. Ti
c. Cu
d. Fe
Electronic configuration of a transition element X in +3 oxidation state is [Ar]3d5 .
What is its atomic number?
a. 25
b. 26
c. 27
d. 24
In the first transition series, the highest B.P. and M.P. is of:
a. Cr
b. V
c. Ni
d. Fe
The tendency of 3d-metal ions to form stable complexes is due to their:
a. Variable oxidation state
b. Strong electronegative nature
c. High charge/size ratio and vacant d-orbitals
d. Very low ionization energies
1(a)
2((b)
3(a)
4(c)
Passage
8
1
2
Lanthanoids show different trends than transition series .In this case; there
is gradual decrease in the atomic as well as ionic radii of the elements along
the series. This is termed as lanthanoid contraction. Due to this there is
change in basic strength of hydroxides in the series. But, in the transition
series, the atomic size of metals remains almost the same.
What is the cause of lanthanoid contraction ?
(a) It is due to poor shielding effects of the electrons present in 4f orbitals.
(b) It is due to poor shielding effects of the electrons present in 4d orbitals
(c) It is due to poor shielding effects of the electrons present in 5f orbitals
(d) None of the above
How do the basic strengths of hydroxides of these vary in a particular
series?
(a) The basic strengths of the hydroxides decreases
(b) The basic strengths of the hydroxides increases
(c) The basic strengths of the hydroxides does not change
(d) None of the above
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3
Answer
Write the general electronic configuration of the elements belonging to fblock.
(a) ns(1-2)
(b) ns2np(1-6)
(c) (n-2)f1-14 (n-1)d 0-1 ns2
(d) None of the above
Ans 1.(a)
Ans 2.(a)
Ans 3.(c)
Passage
9
The f-block elements are those in which the differentiating electrons enters the (n2) f orbitals. There are two series of f-block elements corresponding to filling of 4f and
5f orbitals. The series of 4f orbitals is called lanthanoids. Lanthanoids show different
oxidation states depending upon the stability of f0, f7 and f14 configurations, though the
most common oxidation state is +3. There is a regular decrease in the size of
lanthanoid ions with increase in atomic number which is known as lanthanoid
contraction.
1
Which of the following lanthanoid exhibit +2 oxidation state
(a) Cerium (Z = 58)
(b) Europium ( Z= 63)
(c) Lutetium( Z= 71)
(d)Gadolinium (Z=71)
2
Lanthanoid contraction is due to poor shielding effect of
(a) 6s
(b) 6p
(c) 4f
(d) 5f
Answer
1(b)
2(c)
Passage
In regards to atomic size of transition metals, there is little variation. Typically, when
10
moving left to right across the periodic table, there is a trend of decreasing atomic
radius. However, in the transition metals, moving left to right, there is a trend of
increasing atomic radius which levels off and becomes constant. In the transition
elements, the number of electrons are increasing but in a particular way. The number
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of electrons increase going across a period, thus, there is more pull of these electrons
towards the nucleus. However, with the d−electrons, there is some added electronelectron repulsion. For example, in chromium, there is a promotion of one of the 4s
electrons to half fill the 3d sublevel; the electron-electron repulsions are less and the
atomic size is smaller. The opposite holds true for the latter part of the row.
1
In Fe, Co, Ni, Cu & Zn the metallic radius is the largest in
A. Zn
B. Fe
C. Ni
D. Cu
2
Which of the following statements is false?
A. Zr& Hf have almost similar sizes
B. At the end of each row there is little increase in radii
C. Sc has the biggest size in 1st row
D. Radii gradually decrease along a period in d-block
3
From the graph above it is seen that the atomic radius of Fe is around
A. 11.6 nm
B. 14 nm
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C. 14.5 nm
D. 12.6 nm
Answer
1.A
2. D
3.D
Questions submitted by the PGTs (Chemistry) of KVs of Bhubaneswar,
Guwahati, Kolkata, Ranchi, Silchar and Tinsukia Regions.
Vetted by: Koklata Region