$H_3BO_3$ is

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:

Boron trifluoride on reaction with lithium aluminium hydride in ether gives $LiF$,$AlF_3$ and $X$. $X$ on reaction with $NH_3$ gives $Y$. $Y$ on further heating gives a compound $Z$. The number of $\sigma$-bonds and $\pi$-bonds in $Z$ are $x$ and $y$ respectively. $(x+y)$ is equal to

What is the product formed by the action of caustic soda on aluminium hydroxide?

Give the increasing order of group $13$ elements for atomic radius.

Which of the following statements is $NOT$ correct for potash alum?