Ncert Solutions Chemistry Class 12th

8.12 Electronic configuration of Mn²⁺ is [Ar]¹⁸3d⁵ and Electronic configuration of Fe²⁺ is [Ar]¹⁸ 3d⁶ . It is known that half-filled and fully-filled orbitals are more stable. Therefore, Mn in (+2) state has a half-filled stable configuration, whereas the Fe in +3 oxidation state has partially filled subshells, which are relatively unstable. This is the reason Mn²⁺ shows resistance to oxidation to Mn³⁺. Also, Fe²⁺ has 3d⁶ configuration and by losing one electron, it attains half- filled stable Hence, Mn²⁺ compounds more stable than Fe²⁺ towards oxidation to their +3 state.

Mn+2→

Manganese has the atomic no. 25 and its electronic configuration is [Ar]4s23d5.

∴ Electronic configuration of Mn+2=[Ar]3d5

Fe+2→

Fe has the atomic no. 26 and its electronic configuration is [Ar]4s23d6.

∴ Electronic configuration of Fe+2=[Ar]3d6

8.11  (i) The atomic number of Cr is 24 and the electronic configuration is [Ar] 3d⁵4s^1. When 3 electrons are removed, it becomes Cr³⁺. The electronic configuration of Cr³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ Or [Ar]3d³

(ii) The atomic number of Pm is 61 and the electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s² or [Xe] 4f⁵6s². When 3 electrons are removed, it becomes Pm⁺³, having the electronic configuration,

Pm³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f⁴

Or, [Xe]⁵⁴4f⁴

(iii) The atomic number of Cu is 29 and has the electronic configuration of [Ar] 3d¹⁰4s¹. On removing one electron, the Cu⁺is obtained with the electronic configuration, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ Or [Ar] 3d¹⁰

(iv) The atomic number of Ce is 58 and has the electronic configuration of [Xe] 4f¹5d¹6s². When the valence electrons are removed, the Ce⁴⁺ ion with configuration, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ Or [Xe] is obtained.

(v) The atomic number of Co is 27 and has the electronic configuration of [Ar] 3d⁷4s². When 2 electrons are removed from s-orbital, it becomes Co²⁺with electronic configuration, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ Or, [Ar] 3d⁷.

(vi) The atomic number of Lu is 71 and has the electronic configuration of [Xe] 4f¹⁴5d¹6s². When 2 electrons are removed, Lu²⁺with the configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f ¹⁴ 5d ¹ Or, [Xe] 4f¹⁴5d¹

(vii) The atomic number of Mn is 25 and has the electronic configuration of [Ar] 3d⁵4s² . When 2 electrons are removed, Mn²⁺ ion is obtained and has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ Or, [Ar]¹⁸ 3d¹⁰ .

(viii) The atomic number of Th is 90 and has the electronic configuration of [Rn] 6d² 7s² . When 4 electrons are removed, the electronic configuration becomesTh⁴⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f ¹⁴ 5d ¹⁰ 6s ² 6p ⁶ Or, [Rn]

5.31

Electrophoresis: The movement of colloidal particles under an applied electric potential is called When an electric potential is applied to two platinum electrodes dipping in colloidal solutions the colloidal particle move towards the Oppositely charged electrodes.

Coagulation: The process of settling of colloidal particles is called coagulation. When the charge is removed from colloidal solution somehow, then particle start coagulation and settling due to the force of

Dialysis: It is a process of removing a dissolved substance from AC colloidal solution by means of diffusion through a suitable the animal membrane or parchment paper used as a membrane.

Tyndall Effect: When homogenous solution is placed in a dark and viewed in light beam then if it is viewed from sides it appears visible but if it is viewed from 90° it appears to be dark. This effect is known as Tyndall