Identify the correct statements about the anomalous behaviour of boron.

I. Boron trihalides can form dimeric structures.

II. Boron shows +1 as stable oxidation state.

III. Maximum covalency of boron is four.

IV. Boron does not form $$\mathrm{BF}_6^{6-}$$ ion.

Which of the following is formed when $$\mathrm{SO}_3$$ is absorbed by concentrated $$\mathrm{H}_2 \mathrm{SO}_4$$ ?

Identify the correct statements about boron.

I. It has high melting point.

II. It has high density.

III. It has high electrical conductivity.

IV. B-10 isotope of it has high ability to absorb neutrons.

Assertion (A) HCl gas is dried by passing through concentrated H$$_2$$SO$$_4$$.

Reason (R) HCl gas reacts with NH$$_3$$ that gives white fumes.