Question 1

Which of the following statements about chromium is correct?

Accepted Answer

Chromium(VI) in dichromate (Cr₂O₇²⁻) and chromate (CrO₄²⁻) ions are powerful oxidizing agents due to the high oxidation state.

Question 2

Identify the actinide element that is widely used as nuclear fuel in power plants and has an atomic number of 92.

Accepted Answer

Uranium-235 and Uranium-238 are the primary actinide isotopes used as fissile fuel in nuclear reactors.

Question 3

Which transition metal exhibits variable oxidation states and is commonly used as a catalyst in the Contact process for H₂SO₄ manufacture?

Accepted Answer

Vanadium (V⁵⁺/V⁴⁺) undergoes redox changes and acts as the primary catalyst in the oxidation of SO₂ to SO₃ in the Contact process.

Question 4

Which of the following d-block elements has the electronic configuration [Ar] 3d⁵ 4s² in its ground state?

Accepted Answer

Manganese (atomic number 25) has the configuration [Ar] 3d⁵ 4s², representing a half-filled d-orbital which is relatively stable.

Question 5

What is the primary reason lanthanides are called 'rare earths' despite their relatively high abundance in Earth's crust?

Accepted Answer

Lanthanides are dispersed in nature and occur mixed in ores, making their separation and extraction technologically challenging and costly.

Question 6

Which f-block element has the electronic configuration [Rn] 5f⁶ 7s²?

Accepted Answer

Plutonium has atomic number 94 with configuration [Rn] 5f⁶ 7s².

Question 7

Which of the following transition metals does NOT form stable +3 oxidation state in aqueous solution?

Accepted Answer

Copper readily forms Cu²⁺ but Cu³⁺ is highly unstable in aqueous solution; Cu⁺ and Cu²⁺ are the stable states.

Question 8

The lanthanide contraction results in similar ionic radii for pairs of elements. Which pair demonstrates this effect most clearly?

Accepted Answer

Zirconium and Hafnium have nearly identical ionic radii due to lanthanide contraction causing poor separation in nature.

Question 9

Which of the following d-block elements exhibits the maximum number of oxidation states?

Accepted Answer

Manganese can exhibit oxidation states from +2 to +7, showing the maximum variability among these transition metals.

Question 10

The electronic configuration of Cu²⁺ ion is:

Accepted Answer

Cu has configuration [Ar] 3d¹⁰ 4s¹; removing two electrons gives Cu²⁺: [Ar] 3d⁸.

Question 11

Which lanthanide element is commonly used in nuclear reactors as a neutron absorber?

Accepted Answer

Gadolinium has exceptional neutron absorption properties and is specifically used in control rods of nuclear reactors.

Question 12

Among the first-row transition metals, which element has the highest melting point?

Accepted Answer

Chromium has the highest melting point (1907°C) among first-row transition metals due to strong d-orbital bonding.

Question 13

The colour of [CuCl₄]²⁻ complex ion is yellow-green. This is due to:

Accepted Answer

The colour arises from d-d electronic transitions characteristic of tetrahedral Cu(II) complexes with d⁹ configuration.

Question 14

In the complex [CoF₆]³⁻, cobalt exhibits an oxidation state of +3. Given that F⁻ is a weak field ligand, what is the expected electronic configuration and magnetic behavior of this complex?

Accepted Answer

Co³⁺ has d⁶ configuration; weak field F⁻ ligand causes high spin splitting with t₂g⁵eg¹ arrangement, resulting in 4 unpaired electrons and paramagnetic behavior.

Question 15

The lanthanide contraction causes the ionic radii of lanthanides to decrease across the series. Which of the following statements correctly explains the consequence of lanthanide contraction?

Accepted Answer

Lanthanide contraction causes the 5d elements (Hf, Ta, W, etc.) to have nearly identical sizes to their 4d counterparts, explaining the chemical similarity between elements in these periods.

Question 16

Which of the following d-block elements exhibits the highest number of oxidation states in its compounds?

Accepted Answer

Manganese shows oxidation states from +2 to +7, the maximum among d-block elements due to its half-filled d5 configuration providing stability across multiple oxidation states.

Agniveer Army Technical d & f Block Elements

d & f Block Elements — Practice Questions