[newbie!]

these are problems i;ve had in past paper questions from my course (shapes,properties and rections of molecules). i will try to show working as much as posible , hope you cna help.

1)what is meant by the oxidation of water?
ok oxidation OF water would be the same as reuction BY water right? all my notes say about this is taht water is a weak reducing agent except towards strong oxidising agents

2)point group of IF5
according to google its C2 but i have no idea how. i deduced the shape to be square pyramidal due to the lone pair of electons so it looks like this: http://www.thiel.edu/academics/chemistry/faculty/fheald/Graphics/Mole28.gif then using the flow chart
liner = yes
2+ Cn with n>2? = i would say yes but it must be no

3)which of the following contains a centre of inversion? SiF4 XeF4 XeF5- C2F4 ?
ok so i think it would be XeF4 and C2F2
SiF4 is tetrahedral ruling it out.
XeF4 has 4 bonds and 2 lone pairs so idk the shape would be...?
XeF5 has 5 bonds and 1 lone pair, again dont know the resulting shape
and C2F2 i drew like c=c then 2 fluorines off each carbon