Among the following reactions of hydrogen with halogens, the one that requires a catalyst is :

The number of 2-centre-2-electron and 3-centre -2-electron bonds in B₂H₆, respectively, are :

Good reducing nature of H₃PO₂ is attributed to the presence of :

Correct statements among a to d regarding silicones are :

(a)   They are polymers with hydrophobic character.
(b)   They are biocompatible.
(c)   In general, they have high thermal stability and low dielectric strength.
(d)   Usually, they are resistant to oxidation and used as greases.