CBSE Class 12th Chemistry Chapter 4 - d -and f -Block Elements Important Questions with Answers

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Write the formula of an oxo-anion of Manganese (Mn) in which it shows the oxidation state equal to its group number. (Delhi 2017)

Question 2.

What happens when (NH₄)₂Cr₂O₇ is heated? (Delhi 2017)

Question 3.

Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number. (Delhi 2017)

Question 4.

What happens when (NH₄)₂Cr₂O₇ is heated? (Delhi 2017)

Question 5.

Explain the following observations :
(i) Copper atom has completely filled d orbitals (3d¹⁰) in its ground state, yet it is regarded as a transition element.
(ii) Cr²⁺ is a stronger reducing agent than Fe²⁺ in aqueous solutions. (Comptt. All India 2017)

Question 6.

Explain the following observations :
(a) Silver atom has completely filled d-orbitals (4d¹⁰) in its ground state, yet it is regarded as a transition element.
(b) E⁰ value for Mn³⁺ /Mn²⁺ couple is much more positive than Cr³⁺/Cr²⁺. (Comptt. All India 2017)

Question 7.

Explain the following observations :
(i) Zn²⁺ salts are colourless.
(ii) Copper has exceptionally positive \(\mathbf{E}_{\mathbf{M}^{2+} / \mathbf{M}}^{\mathbf{0}}\) value. (Comptt. All India 2017)

Question 8.

A mixed oxide of iron and chromium is fused with sodium carbonate in free access of air to form a yellow coloured compound (A). On acidification the compound (A) forms an orange coloured compound (B), which is a strong oxidizing agent. Identify compound (A) and (B). Write chemical reactions involved. (Comptt. All India 2017)

Question 9.

(a) Give reasons for the following:
(i) Compounds of transition elements are generally coloured.
(ii) MnO is basic while Mn₂O₇ is acidic.
(iii) Calculate the magnetic moment of a divalent ion in aqueous medium if its atomic number is 26. (Comptt. All India 2017)

Question 10.

(a) Account for the following:
(i) Transition metals form large number of complex compounds.
(ii) The lowest oxide of transition metal is basic whereas the highest oxide is amphoteric or acidic.
(iii) E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compared to Cr³⁺/Cr²⁺.
(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements. (Delhi 2017)

Question 1.

(a) (i) How is the variability in oxidation
states of transition metals different from that of the p-block elements?
(ii) Out of Cu⁺ and Cu²⁺, which ion is unstable in aqueous solution and why?
(iii) Orange colour of Cr₂O₇^2- ion changes to yellow when treated with an alkali. Why?
(b) Chemistry of actinoids is complicated as compared to lanthanoids. Give two reasons. (Delhi 2017)

Question 2.

(a) Account for the following:
(i) Transition metals show variable oxidation states.
(ii) Zn, Cd and Hg are soft metals.
(iii) E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compared to Cr³⁺/Cr²⁺.
(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements. (All India 2017)

Question 3.

(a) Following are the transition metal ions of 3d series:
Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺
(Atomic numbers: Ti = 22, V= 23, Mn = 25, Cr = 24)
Answer the following:
(i) Which ion is most stable in an aqueous solution and why?
(ii) Which ion is a strong oxidising agent and why?
(iii) Which ion is colourless and why?
(b) Complete the following equations: (All India 2017)
Important Questions for Class 12 Chemistry Chapter 8 The d- and f-Block Elements Class 12 Important Questions 36

Question 4.

When chromite ore is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (A) is obtained. On acidifying the yellow solution with sulphuric acid, compound (B) is crystallised out. When compound (B) is treated with KC1, orange crystals of compound (C) crystallise out. Identify (A), (B) and (C) and write the reactions involved. (Comptt. Delhi 2017)

Question 5.

(a) (i) Which transition element in 3d series has positive E⁰_M²⁺/M and why?
(ii) Name a member of lanthanoid series which is well know to exhibit +4 oxidation state and why?
(b) Account for the following :
(i) The highest oxidation state is exhibited in oxoanions of transition metals.
(ii) HCl is not used to acidify KMnO₄ solution.
(iii) Transition metals have high enthalpy of atomisation. (Comptt. Delhi 2017)

Question 6.

When chromite ore FeCr₂O₄ is fused with NaOH in presence of air, a yellow coloured compound (A) is obtained which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KC1 forms an orange coloured crystalline compound (C).
(i) Write the formulae of the compounds (A), (B) and (C).
(ii) Write one use of compound (C). (Delhi 2016)

Question 7.

Complete the following chemical equations: (Delhi 2016)
Important Questions for Class 12 Chemistry Chapter 8 The d- and f-Block Elements Class 12 Important Questions 11

Question 8.

Give reasons :
(i) Transition metals show variable oxidation, states.
(ii) Actinoids show wide range of oxidation states. (Comptt. Delhi 2016)

Question 9.

Give reasons :
(i) Zn is not regarded as a transition element.
(ii) Cr²⁺ is a strong reducing agent. (Comptt All India 2016)

Question 10.

Give reasons:
(i) Mn shows the highest oxidation state of +7 with oxygen but with fluorine it shows the highest oxidation state of +4.
(ii) Transition metals show variable oxidation states.
(iii) Actinoids show irregularities in their electronic configurations. (Delhi 2016)