[newbie!]

from a course titled "evironmental and analytical chemistry" obv. the analytial part but idk how "analytical" it actually is.
we focussed on 3 elements - Xe, Boron and Si

1) Explain how the silicon to oxygen ratio in minerals gives important clues as to the connectivity of the SiO4 tetrahedra in the structure in question. Illustrate your answer with examples of real compounds.
[10]
all i know is it represents long infinite chains based on the SO4 polyhedra. different ratios give different structures eg) benitoite has 1:3 ratio
1:2.5 ratio means its sheet like

2) Use Wade’s rules to predict the structures of B4H8[Fe(CO)3] and sketch its atomic arrangement. (note Fe(CO)3 is a 2-skeletal-electron species)
valence e- = 22
-8 for 4BH bonds taking up 2 e- leaves 14e- (7 skeletal pairs)
but then thats BnHn+4 n+3 skeletal pairs.
the rules are BnHn+4 - nido
n+3 skeletal pairs - arachno.
so whihc? i think i may have done somthing wrong?

3)Use the VSEPR model (show your reasoning) to predict the shapes of [XeF5]+
ve = 42 so its Xe with 5 F's coming off and a lone pair. would it be trigonal bipyramidal?

hope you can help