What happens when
(a) Borax is heated strongly,
(b) Boric acid is added to water,
(c) Aluminium is treated with dilute NaOH,
(d) `BF_(3)` is reacted with ammonia ?

Explanation

a.When borax is strongly heated, a transparent glassy bead which consists of sodium metaborate and boric anhydride is formed.
`underset("Borax")(Na_(2)B_(4)O_(7).10H_(2)O)overset(Delta)toNa_(2)B_(4)O_(7)+10H_(2)O`
`Na_(2)B_(4)O_(7)underset("Red Heat")overset(Delta)tounderset(ubrace({:(" Sodium, Boric"),("metaborate, anhydride"):})_("Transport glassy bead"))(2NaBO_(2)" + "B_(2)O_(3))`
b. Boric acid behaves as a Lewis acid and hence accepts `overset(ө)OH` ion form `H_(2)O` and realeses `H^o+` in the solution.
c. `2Al_((s))+underset(("dil"))(NaOH_((aq)))+6H_(2)Oto2Na^(o+)[Al(OH)_(4)]_((aq))^()+3H_(2(g)) or underset("Sodium meta-aluminate(III)")(Na_(2)AlO_(2).2H_(2)O)`
d.`F_(3)B+:NH_(3)to[F_(3)Blarr:NH_(3)]`
`BF_(3)` is a Lewis acid and accepts a pair of electron from `N` of `NH_(3)` molecule to form an adduct,
`[F_(3)Blarr:NH_(3)]`