Unit 4: d- and f-Block Elements Chemistry Previous year questions PYQ

Unit 4: d- and f-Block Elements

Part A: d-Block Elements (Transition Metals)

1. General Introduction

The d-block elements are found in groups 3 to 12 of the periodic table. These elements have partially filled d-orbitals either in ground state or in one of their oxidation states.

2. Electronic Configuration

The general configuration of d-block elements is:

[Noble Gas] (n-1)d^1-10 ns^0-2

• First row (3d series): Sc (Z=21) to Zn (Z=30)
• Second row (4d series): Y (Z=39) to Cd (Z=48)
• Third row (5d series): La (Z=57), Hf (Z=72) to Hg (Z=80)

3. Occurrence and Characteristics

• Mostly found in ores like oxides, sulphides, and halides.
• Good conductors of heat and electricity.
• Exhibit variable oxidation states.
• High melting and boiling points.

4. General Trends in Properties (First Row)

(a) Metallic Character

All are metals, show malleability, ductility, conductivity, and luster.

(b) Ionization Enthalpy

Relatively high due to nuclear attraction, but lower than s- and p-block elements.

(c) Oxidation States

These elements show variable oxidation states due to participation of (n-1)d and ns electrons.

• Fe: +2, +3
• Mn: +2 to +7

(d) Ionic Radii

Decrease across the period due to increased nuclear charge → stronger pull on electrons.

(e) Colour

Many transition metal ions are coloured due to d-d electron transitions.

(f) Catalytic Properties

• Transition metals and their compounds act as good catalysts (e.g., Fe in Haber process).

(g) Magnetic Properties

Paramagnetic due to unpaired d electrons. Magnetic moment:

μ = √[n(n+2)] BM

where n = number of unpaired electrons.

(h) Interstitial Compounds

• Small atoms like H, B, C, N occupy voids in metal lattice (e.g., TiC, Fe₃H).

(i) Alloy Formation

Transition metals form strong and hard alloys (e.g., brass = Cu + Zn).

5. Important Compounds

Potassium Dichromate (K₂Cr₂O₇)

• Preparation: From chromite ore.
• Properties: Orange crystals, strong oxidising agent in acidic medium.

Potassium Permanganate (KMnO₄)

• Preparation: From pyrolusite (MnO₂).
• Properties: Deep purple, strong oxidising agent in acidic, neutral, and basic media.

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Part B: f-Block Elements

1. Lanthanides (4f Series)

Electronic Configuration

General: [Xe] 4f^1–14 5d^0–1 6s²

Oxidation States

+3 is most common; some show +2 or +4 (e.g., Ce⁺⁴, Eu⁺²).

Chemical Reactivity

• Reactive, especially with water and acids.
• Form ionic, basic oxides.

Lanthanide Contraction

Gradual decrease in size of atoms and ions across the lanthanide series due to poor shielding by 4f electrons.

Consequences of Lanthanide Contraction

• Similarity in properties of second and third-row transition elements (Zr ~ Hf).
• Separation of lanthanides becomes difficult.

2. Actinides (5f Series)

Electronic Configuration

General: [Rn] 5f^1–14 6d^0–1 7s²

Oxidation States

More variable than lanthanides, ranging from +3 to +6 (e.g., U⁺⁶).

Comparison with Lanthanides

• Actinides are more reactive.
• Show greater oxidation state variability.
• Radioactive in nature.

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Tips for Teaching Effectively:

• Use periodic table handouts to visualize positions of d and f block.
• Compare properties across rows to reinforce trends.
• Demonstrate oxidation reactions of KMnO₄ and K₂Cr₂O₇ with common reducing agents.
• Explain magnetic properties using diagrams of d-orbital filling.
• Use mnemonic devices to help remember lanthanide series (e.g., "La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu").

Interactive Simple Harmonic Motion (SHM)

x(t) = 50 sin(1t + 0)

Amplitude (A): 50
Angular Frequency (ω): 1
Phase (ϕ in radians): 0

Equation of Cirlce

Interactive Equation of a Circle

(x - 0)² + (y - 0)² = 50²

Center X (h): 0
Center Y (k): 0
Radius (r): 50

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MCQ SET 01 Physics Class 11

Section – A: Multiple Choice Questions

Question 1:

Which of the following is the correct representation of a 10 cm long scale?

(A) The scale of the length is 10 cm.
(B) This is a 10 cm long scale.
(C) This is a 10 cm long scale.
(D) The scale of the length is 10 c.m.

Answer: (A) The scale of the length is 10 cm.

Explanation: Units should be symbolically represented without dots unless they appear at the end of a sentence as a full stop.

Question 2:

The displacement (in meters) of a body varies with time t (in seconds) as x = t² - 2t - 3. The displacement is zero for a positive value of t equal to:

(A) 1 s
(B) 4 s
(C) 3 s
(D) 2 s

Answer: (C) 3 s

Explanation: Given x = t² - 2t - 3. For x = 0, 0 = (t + 1)(t - 3) so t = 3, -1.

Question 3:

If A = B + C and the magnitudes of A, B, and C are 5, 4, and 3, respectively, then the angle between A and C is:

(A) sin^-1 (3/5)
(B) cos^-1 (3/5)
(C) cos^-1 (4/5)
(D) sin^-1 (4/5)

Answer: (B) cos^-1 (3/5)

Question 4:

Application of lubricants cannot reduce:

(A) Static friction
(B) Sliding friction
(C) Rolling friction
(D) Inertia

Answer: (D) Inertia

Question 5:

A force of 49 N is just able to move a block of mass 10 kg on a rough horizontal surface. The coefficient of friction is:

(A) 0.5
(B) 1.0
(C) 0
(D) 0.8

Answer: (A) 0.5

Question 6:

When a body is dropped from a tower, then there is an increase in its:

(A) Weight
(B) Acceleration
(C) Velocity
(D) Gravitational potential energy

Answer: (C) Velocity

Question 7:

A cyclist comes to a skidding stop in 20 m. During this process, the force on the cycle due to the road is 100 N and is directly opposed to the motion. Work done by the road on the cycle is:

(A) -2000 J
(B) 2000 J
(C) 1000 J
(D) 100 J

Answer: (A) -2000 J

Question 8:

On which of the following factors does the moment of inertia of an object not depend?

(A) Axis of rotation
(B) Angular velocity
(C) Distribution of mass
(D) Mass of an object

Answer: (B) Angular velocity

Question 9:

Escape velocity of an object of mass m is proportional to:

(A) m²
(B) m
(C) m^-1
(D) m⁰

Answer: (D) m⁰

Question 10:

Rigidity modulus and Young’s modulus are respectively η and Y. A copper wire of length L and area of cross-section A is pulled so that its length becomes 5L and area of cross-section becomes A/5. So:

(A) Y increases, η decreases.
(B) η increases, Y decreases.
(C) Both Y and η increase.
(D) Both Y and η remain unchanged.

Answer: (D) Both Y and η remain unchanged.