Aluminium reacts with caustic soda to form

How would you explain the lower atomic radius of $Ga$ as compared to $Al$?

Boron does not form $B^{3+}$ cation easily. It is due to

Two students were given the task to prepare an adduct $NH_3 \to BH_3$ at low temperature :-
Student $I$ :- She mixed $B_2H_6$ and $NH_3$
Student $II$ :- He mixed $B_2H_6$ with $THF$ followed by addition of $NH_3$
Which student is expected to get the $CORRECT$ final product?

Aluminium reacts with dilute $HCl$ and liberates a gas '$A$' and with aqueous alkali liberates a gas '$B$'. $A$ and $B$ respectively are

Why does boron trifluoride $(BF_3)$ behave as a Lewis acid?