Which of the following sublimes on heating?

Which one of the following is the correct statement?

Draw the structures of $BCl_3.NH_3$ and $AlCl_3$ (dimer).

The reason for boric acid being polymeric is .....

Which of the following statements is correct?

The correct statements from the following are $:$
$(A)$ $Tl^{3+}$ is a powerful oxidising agent
$(B)$ $Al^{3+}$ does not get reduced easily
$(C)$ Both $Al^{3+}$ and $Tl^{3+}$ are very stable in solution
$(D)$ $Tl^{+}$ is more stable than $Tl^{3+}$
$(E)$ $Al^{3+}$ and $Tl^{+}$ are highly stable
Choose the correct answer from the options given below $:$