Which one of the following compounds of Group-$14$ elements is not known?

Statement I : $\alpha$ and $\beta$ forms of sulphur can change reversibly between themselves with slow heating or slow cooling.

Statement II : At room temperature the stable crystalline form of sulphur is monoclinic sulphur.

In the light of the above statements, choose the correct answer from the options given below:

Among the following, the number of halide(s) which is/ are inert to hydrolysis is

(A) ${\mathrm{BF}}_3$
(B) ${\mathrm{SiCl}}_4$
(C) ${\mathrm{PCl}}_5$
(D) ${\mathrm{SF}}_6$

Given below are two statements:
Statement $\mathrm{I}:$ Colourless cupric metaborate is reduced to cuprous metaborate in a luminous flame.

Statement $\mathrm{II}:$ Cuprous metaborate is obtained by heating boric anhydride and copper sulphate in a non-luminous flame.

In the light of the above statements, choose the most appropriate answer from the options given below.

Given below are the statements about diborane
(a) Diborane is prepared by the oxidation of ${\mathrm{NaBH}}_4$ with ${\mathrm{I}}_2$
(b) Each boron atom is in ${\mathrm{sp}}^2$ hybridized state
(c) Diborane has one bridged $3$ centre-$2$-electron bond
(d) Diborane is a planar molecule

The option with correct statement(s) is