If $\mathrm{B}–\mathrm{Cl}$ bond has a dipole moment, explain why ${\mathrm{BCl}}_3$ molecule has zero dipole moment.

Give the reason, why a mixture of dilute $\mathrm{NaOH}$ and aluminium pieces is used to open drain.

When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of $\mathrm{NaOH}$ to give soluble complex (B). Compound (A) is soluble in dilute $\mathrm{HCl}$ to form compound (C). The compound (A) when heated strongly gives (D), which is used to extract metal. Identify (X), (A), (B), (C) and (D). Write suitable equations to support their identities.

The type of hybridisation of boron in diborane is

Give reason why: Aluminium wire is used to make transmission cables.