Account for the following observations: (i) AlCl3 is a Lewis acid (ii) Though fluorine is more electronegative than chlorine yet BF3 is a weaker Lewis acid than BCl3 (iii) PbO2 is a stronger oxidising agent than SnO2 (iv) The +1 oxidation state of thallium is more stable than its +3 state

This is a Long Answers Type Questions as classified in NCERT Exemplar (i) ln? AlCl3, Aluminium is bonded to 3 chlorine atoms through three covalent bonds and six electrons are shared in the structure. To have complete Octet, AlCl3 lacks two electrons & hence act as an electron acceptor substance or Lewis acid. (ii) Undoubtedly, fluorine has more electronegativity than chlorine, BF3 is stronger Lewis acid than BCl3 because of n−p π back bonding in BF3, both the constituting atoms boron and fluorine are involve p-orbital in back bonding. On moving down the group, the size of halogen atoms increases, back bonding decreases and Lewis acid character also decreases. (iii) PbO2, lead is in +2 oxidation state and can be reduced to its most stable oxidation state of +2. Hence PbO2 can be further exidised or act as a strong oxidising agent. and in SnO, Sn is and +2 oxidation state and can extend its oxidation state up to +4. Thus, SnO can be used as a reducing agent. (iv) As we move down the group in group 13 the participation of s-electrons in bond formation decreases the primary reason behind this is the inert pair effect. In this the p-electrons take part in bond formation and more energy is required to unpair the valence electrons to make them participate in bonding. Due to this the lower oxidation state of elements becomes stable than the higher oxidation state. As for thallium, +1 oxidation state is more stable than +3.

Account for the following observations:

(i) AlCl₃ is a Lewis acid (ii) Though fluorine is more electronegative than chlorine yet BF₃ is a weaker Lewis acid than BCl₃

_(iii)_{PbO2 is a stronger oxidising agent than SnO2}_(iv)_{The +1 oxidation state of thallium is more stable than its +3 state}

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Alok Kumar Singh | Contributor-Level 10

8 months ago

This is a Long Answers Type Questions as classified in NCERT Exemplar

(i) ln? AlCl₃, Aluminium is bonded to 3 chlorine atoms through three covalent bonds and six electrons are shared in the structure. To have complete Octet, AlCl₃lacks two electrons & hence act as an electron acceptor substance or

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Chemistry NCERT Exemplar Solutions Class 11th Chapter Eleven 2025

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(i) Boron in [B(OH)₄]⁻	(a) sp²
(ii) Aluminium in [Al(H₂O)₆]³⁺	(b) sp³
(iii) Boron in B₂H₆	(c) sp³d²
(iv) Carbon in Buckminsterfullerene
(v) Silicon in SiO₄⁴⁻
(vi) Germanium in [GeCl₆]²⁻

Column I	Column II
(i) Diborane	(a) Used as a flux for soldering metals
(ii) Gallium	(b) Crystalline form of silica
(iii) Borax	(c) Banana bonds
(iv) Aluminosilicate	(d) Low melting, high boiling, useful for measuring high temperatures
(v) Quartz	(e) Used as catalyst in petrochemical industries.

Column I	Column II
(i) BF₄⁻	(a) Oxidation state of central atom is +4
(ii) AlCl₃	(b) Strong oxidising agent
(iii) SnO	(c) Lewis acid
(iv) PbO₂	(d) Can be further oxidised
	(e) Tetrahedral shape