Case Study Questions for Class 12 Chemistry Chapter 8 The d- and f-Block Elements

There is Case Study Questions in class 12 Chemistry in session 2020-21. For the first time, the board has introduced the case study questions in the board exam. The first two questions in the board exam question paper will be based on Case Study and Assertion & Reason. The first question will have 5 MCQs out of which students will have to attempt any 4 questions. The second question will carry 5 Assertion & Reason type questions with the choice to attempt any four. Here are the questions based on case study.

Case Study Question 1:

Read the passage given below and answer the following questions:

The f-block elements are those in which the differentiating electrons enters the (n-2)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 lanthanides. Lanthanides show different oxidation states depending upon stability of f⁰, f⁷ and f¹⁴ configurations, though the most common oxidation states is +3. There is a regular decrease in the size of lanthanides ions with increase in atomic number which is known as lanthanides contraction.

The following questions are multiple choice question. Choose the most appropriate answer:

(i) The atomic number of three lanthanides 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

(ii) lanthanide contraction is observed in
(a) Gd
(b) At
(c) Xe
(d) Te

(iii) Which of the following is not the configuration of lanthanide?
(a) [Xe]4f¹⁰6s²
(b) [Xe]4f¹⁵d¹6s²
(c) [Xe]4d¹⁴5d¹⁰6s²
(d) [Xe]4f⁷5d¹6s²

Or

Name a member of the lanthanide series which is well known to exhibit +4 oxidation state.
(a) Cerium (X=58)
(b) Europium (Z=63)
(c) Lanthanum (Z=57)
(d) Gadolinium (Z=64)

(iv) Identify the incorrect statement among the following.
(a) Lanthanide contraction is the accumulation of successive shrinkages.
(b) the different radii of Zr and Hf due to consequences of the lanthanide 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

Answer

(i) a
(ii) a
(iii) c
or a
(iv) b