In which of the following reaction, the hybridisation of the central atom changes from $sp^2$ to $sp^3$ ?

Select the incorrect statement

$(a)$ $PCl_5$ form weak monobasic acid during hydrolysis
$(b)$ In $B_3N_3H_6$ nucleophile attack on $B-$ atom
$(c)$ $Al_2Cl_6$ is a polar and planar molecule
$(d)$ In $AlF_3$, hybridisation of $Al$ is $sp^2$

The stability of $+ 1$ oxidation state among $Al,Ga, In$ and $Tl$ increases in the sequence

The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is :- 

Aluminium trifluoride is insoluble in anhydrous $HF$ but dissolves on addition of $NaF$. Aluminium trifluoride precipitates out of the resulting solution when gaseous $BF $$_{3}$ is bubbled through. Give reasons.