Which of the following is not correct ?

detailed solution

Correct option is D

→ Monomeric trihalide [ AlCl3 ] is lewis acid . AlCl3 is electron deficient and hence in order to get octet configuration the central atom "Al" accepts the electron pair and shows lewis acidic character.→ Sizes of Al and Cl are large, therefore in between  Al and Cl "π" bond formation is not possible.In order to get octet configuration around the "Al" AlCl3 undergoes dimerisation and forms Al2Cl6  dimer.∴ AlCl3 achieves stability by forming a dimer.→ Anhydrous AlCl3 fumes in air.White fumes appear around the bottle of anhydrous aluminium chloride. Anhydrous aluminium chloride is partially hydrolysed with atmospheric moisture to liberate HCl gas. Moist HCl appears white in colour.                           OR→TlI3 cannot exist in nature and it is highly unstable,Reason :Due to inert pair effect Tl forms only Tl (+I) compounds and cannot forms Tl(+III)compounds.For "Tl" +1 oxidation state is more stable,due to inert pair effect.NOTE: For IIIA group higher oxidation state is due to involvement of ns and np electrons.                IIIA group ns2  np1         +3 oxidation stateLower oxidation state is due to involvement of only valency "np" electrons.              IIIA group ns2 np1      +1 oxidation stateHigher oxidation state stability decreases from top to bottom.Lower oxidation state stability increases from top to bottom.Stability order of +3 oxidation state: B+3 >Al+3 > Ga+3  > In+3  >Tl+3Stability order of +1 oxidation state: B+ > Al+ >Ga+1  > In+1 >Tl+1Therefore, Tl+3 is acting as strong oxidising agent.Due to poor shielding effect by the innershell f- and d-orbitals electrons ,the valency s-orbial electrons are strongly held by the nucleus,therefore valency s-orbital electron pair does not involve in bonding [inert pair] and hence only one p-orbital electron involves in bonding and shows mainly +1 oxidation state.  Hence +1 oxidation state is stable for Tl is due to inert pair effect.