Which of the following substances is the strongest acid?

Given below are two statements:
Statement $I$: Aluminium is more electropositive than thallium as the standard electrode potential value of $E^\circ_{Al^{3+}/Al}$ is negative and $E^\circ_{Tl^{3+}/Tl}$ is positive.
Statement $II$: The sum of first three ionization enthalpies of boron is very high when compared to that of aluminium. Due to this reason,boron forms covalent compounds only and aluminium forms $Al^{3+}$ ion.

Which of the following is a non-metal?

In the given structure of Diborane,$\theta_1$ and $\theta_2$ are respectively:

In borax,the number of $B-O-B$ links and $B-OH$ bonds present are,respectively:

The number of neutrons present in the more abundant isotope of boron is $x$. Amorphous boron upon heating with air forms a product,in which the oxidation state of boron is $y$. The value of $x+y$ is ...