True / False
(a) `BCl_(3)` in aqueous solution exists as `B^(3+)` and `Cl^(-)`
(b) Pure crystalline boron is very unreactive and it is attacked only at high temperatures by strong oxidising agents such as a mixture of hot concentrated `H_(2)SO_(4)` and `HNO_(3)`
( c) `AIX_(3)(X=Cl,Br)` exists as dimer and retains dimar formula in non-polar solvents like ether, benzene etc.
(d) `Be_(2)C` is called acetylide because it reacts with water yielding ethyne.
(e) `Pb_(3)O_(4)` a double oxide, is obtained by heating lead `(II)` oxide in air.

Answer

(a)False , (b)True , ( c)True , (d)False , (e)True

Explanation

(a)Statement is incorrect. `BCl_(3)` hydrolses in aqueous solution to give boric acid.Because it has large ionisation energies and to make the enthalpy of solution of `BCl_(3)` negative, the enthalpy of hydration of `B^(3+)` should be very high `(~ 600 g kJ)` which is unlikely for the small `B^(3+)` cation.
(b)`2B+6HNO_(3)(aq.)to2H_(3)BO_(3)(aq.)+6NO_(2)(g)`
( c)Statement is correct and its dimer structure is as follows.It acquires this structure for attaining an octet of electrons.Dimer formula retains in non-polar solvent like ether, benzene

(d)Statement is incorrect as it is methanide because it gives methane on reaction with water.
`Be_(2)C+4H_(2)Oto2Be(OH)_(2)+CH_(4)`
(e)`3PbO+O_(2)overset(Delta)toPb_(3)O_(4)`