Explain why the 100 grams of ice would have a greater volume than 100 grams of water

There is no logical reason for it.  Every substance known gets smaller
when it freezes from the liquid form to the solid form, and for every
substance, a lump of it sinks to the bottom in a bottle of it.

Except for one unusual known substance . . . water !
The only known substance that gets bigger when it freezes.

That's why ice cubes float in your soda, that's why icebergs
float in the ocean, that's why a full bottle of water cracks in
the freezer, and that's why water that seeps into the crack in
a rock can chip pieces off of the rock in the Winter.  

An interesting factoid, to amuse and amaze your friends with.

And also, by the way, if water didn't do that, then life on Earth
would not be possible.



The real reason for it has to do with the shape of the water molecule
and where the valence electron from the hydrogen atom goes and
stuff like that.  I don't know anything about that stuff.