Boron forms $BX_3$ type of halides. The correct increasing order of Lewis-acid strength of these halides is

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.

During metallurgy of aluminium bauxite is dissolved in cryolite because

Complete the following chemical equations :

$Z + 3LiAl{H_4} \to X + 3LiF + 3Al{F_3}$

$X + 6{H_2}O \to Y + 6{H_2}$

$3X + 3{O_2}\xrightarrow{\Delta }{B_2}{O_3} + 3{H_2}O$