The Lewis acid character of boron tri halides follows the order:

Which one is used as a bye-product in Serpeck's process

$N{a_2}{B_4}{O_7}\xrightarrow{x}{H_3}B{O_3}\xrightarrow{\Delta }{B_2}{O_3}\xrightarrow{y}B$

Here $X, Y$ are respectively

The tendency of $BF_3, BCl_3$ and $BBr_3$ to behave as Lewis acid decreases in the sequence

Give reasons:

$(i)$ Conc. $HNO _{3}$ can be transported in aluminium container.

$(ii)$ $A$ mixture of dilute $NaOH$ and aluminium pieces is used to open drain.

$(iii)$ Graphite is used as lubricant.

$(iv)$ Diamond is used as an abrasive.

$(v)$ Aluminium alloys are used to make aircraft body.

$(vi)$ Aluminium utensils should not be kept in water overnight.

$(vii)$ Aluminium wire is used to make transmission cables.