Which metal is protected by a layer of its own oxide?

$BCl_3 + H_2O \longrightarrow$ Product,here product is:

Which of the following is only acidic in nature?

Aluminium $(III)$ chloride forms a dimer because ........

Given below are two statements:
Statement $I$: Boron is extremely hard,indicating its high lattice energy.
Statement $II$: Boron has the highest melting and boiling point compared to its other group members.
In the light of the above statements,choose the most appropriate answer from the options given below:

The formation of $Al_2O_3$ is accompanied by the release of a large amount of energy. This property is utilized in which of the following?