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}

<p>This is a Long Answers Type Questions as classified in NCERT Exemplar</p><p><strong> (i) </strong>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 &amp; hence act as an electron acceptor substance or Lewis acid.</p><p><strong> (ii) </strong>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.</p><p>&nbsp;</p><p><strong>_(iii)</strong>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.</p><p>&nbsp;</p><p><strong>_(iv)</strong>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.</p><p>&nbsp;</p>

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