Q.Which among the following is not a borane?

Diborane, B₂H₆, the simplest borane, is made industrially by treating boron trifluoride with sodium hydride around 450 K (2BF₃ + 6NaH → B₂H₆ + 6NaF), trapping the product immediately to prevent further pyrolysis; small-scale routes include reacting iodine with sodium borohydride in diglyme, and heating magnesium boride with HCl (which gives a mixture of volatile boranes from which B₂H₆ can be isolated).

It is a colourless, extremely toxic, sweet-smelling, highly reactive gas of low thermal stability that progressively converts to higher boranes on heating, liberating hydrogen at each step, and ultimately decomposes to the elements if heated red-hot. It reacts with water/alkali to give boric acid/metaborate; pure diborane does not react with air at room temperature, but the impure gas ignites explosively, releasing a large amount of heat (ΔH = -2165 kJ mol⁻¹) to give B₂O₃. With methanol it gives trimethyl borate.

Diborane adds across alkenes and alkynes in ether (hydroboration, Section 2.2.6, widely used for anti-Markovnikov addition in synthetic organic chemistry); with ionic hydrides it gives metal borohydrides (LiBH₄, NaBH₄); and with excess ammonia at low temperature it gives a diammoniate adduct that, on further heating in a closed vessel, converts to borazole (borazine, B₃N₃H₆), the six-membered B-N ring often called 'inorganic benzene'.

Uses: a high-energy propellant fuel, a reducing agent in organic chemistry, and in welding torches.