Chemistry Class 12 NCERT Solutions: Chapter 8 the D and F Block Elements Part 7 (For CBSE, ICSE, IAS, NET, NRA 2023)

Get top class preparation for CBSE/Class-12 right from your home: get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-12.

Q: 27. What are alloys? Name an important alloy, which contains some of the lanthanoid metals. Mention its uses.


An alloy is a solid solution of two or more elements in a metallic matrix. It can either be a partial solid solution or a complete solid solution. Alloys are usually found to possess different physical properties than those of the component elements.

An important alloy of lanthanide s is Mischmetal. It contains lanthanoids , iron .


(1) Mischmetal is used in cigarettes and gas lighters.

(2) It is used in flame throwing tanks.

(3) It is used in tracer bullets and shells.

Q: 28. What are inner transition elements? Decide which of the following atomic numbers are the atomic numbers of the inner transition elements: .


Inner transition metals are those elements in which the last electron enters the orbital. The elements in which the and the orbitals are progressively filled are called f-block elements. Among the given atomic numbers, the atomic numbers of the inner transition elements are .

Q: 29. The chemistry of the actinoid elements is not so smooth as that of the Lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.


Lanthanoids primarily show three oxidation states . Among these oxidation states, state is the most common. Lanthanoids display a limited number of oxidation states because the energy difference between and orbitals is quite large. On the other hand, the energy difference between and orbitals is very less. Hence, actinoids display a large number of oxidation states. For example, uranium and plutonium display , and oxidation states while neptunium displays , and . The most common oxidation state in case of actinoids is also .

Q: 30. Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.


The last element in the actinoid series is lawrencium, . Its atomic number is and its electronic configuration is . The most common oxidation state displayed by it is ; because after losing electrons it attains stable configuration

Q: 31. Use Hund՚s rule to derive the electronic configuration of ion and calculate its magnetic moment on the basis of ‘spin-only’ formula.


Magnetic moment can be calculated as:


number of unpaired electrons



Q: 32. Name the members of the lanthanoid series which exhibit oxidation state and those which exhibit oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.


The lanthanides that exhibit and states are shown in the given table. The atomic numbers of the elements are given in the parenthesis.

Q_32_The Members of the Lanthanoid Series

Ce after forming attains a stable electronic configuration of .

Tb after forming attains a stable electronic configuration of .

after forming attains a stable electronic configuration of .

after forming attains a stable electronic configuration of .