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 heated strongly, a transparent glassy bead which consis of sodium metaborate `(NaBO_(2))` and boric anhydride is formed
`underset(" Borax ")(Na_(2)B_(4)O_(7).10H_(2))overset("Heat")rarrNa_(2)B_(4)O_(7) + 10H_(2)O`

(b) Boric act as a weak Lewis acid by accepting a hydroxide ion of water and releasing a proton the solution.

(c ) Dihydrogen is evolved.
`2Al (s) + 2NaOH(aq) + 6H_(2)O(l) rarr 2Na^(+) [Al(OH)_(4)]^(-) + 3H_(2)(g)`
(d) `BF_(3)` being a Lewis acid accepts a pair of electrons from `NH_(3)` to form the corresponding complex.