>>>     Of course for the water to be any good, it has to be in liquid form.
>
>> You're aware that (on Earth) there are organisms that live in solid ice,
>> right?
>
>    They did not originate in ice. The simply adapted to it afterwards.

That's true. It's also true that planets that are far from the Sun right 
now might have been nearer at some point. Or the Sun's output may have 
changed.

But ultimately, yes, it seems more plausible that life would originate 
and thrive in a liquid or possibly vapour environment, rather than a 
solid one. (I have no idea whether it's feasible in plasma.)

>> What makes you think that chemicals which are "rare" on Earth would
>> necessarily be rare elsewhere?
>
>    There would have to be a significantly different process that formed
> those rare elements than here on Earth. What would that process be?

A cursory glance at the chemical composition of the surface or 
atmosphere of various planets around us indicates wildly differing 
chemistry. I don't know enough about planet formation to speculate as to 
why. (Presumably different elements get transported to different places 
or something...)

>>> (Also, most liquids other than water get denser when they
>>> solidify, which is a big problem.)
>
>> Care to explain why?
>
>    If water had a higher density when it freezes (as happens with the vast
> majority of other chemical compounds), life on Earth wouldn't exist because
> all bodies of water would freeze from the bottom up, killing all living
> organisms.

OK. But presumably that's only "a big problem" if the chemical we're 
talking about has a solid phase that can potentially exist on the planet 

your hypothetical planet never gets that cold, the fact that solid 
ammonia is more dense than liquid ammonia shouldn't be a problem.

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