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'A mixture is where two or more mixtures are mixed together, the elements forming the mixture still retain their properties and therefore a mixture is just a 'salad bowl' of different chemical properties.'

OR

'A mixture is where two or more mixtures are mixed together. The elements forming the mixture still retain their properties and therefore a mixture is just a 'salad bowl' of different chemical properties.'

There aren't any differences except the period in front of 'the' in the first line.
Comments  
Hello, JK!
I definitely prefer the second one, although I think a semicolon would have done the job.Maybe also a comma between "properties" and "and"?
I realize the question was about punctuation, but I couldn't help noticing something else.

When defining a term ("mixture" in this case), it's not at all usual to use the same term within the definition. How about saying, "A mixture is a combination of two or more substances"? Otherwise we're left with something a little like "A mixture is a mixture of mixtures", right?

CJ
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How about

'A mixture is where two or more elements are mixed together, the elements forming the
mixture still retain their properties. Therefore a mixture is just a 'salad bowl' of different chemical properties.' ?

How does that sound?

I find the sentence not that well balanced. The comma between "together" and "the elements" isn't enough. Moreover, I think there are too many mix-words...
I quite like MrP.'s "A mixture is a combination of two or more substances"
Maybe you could go on like this:
... substances where each element retains its properties;/. t/Therefore etc...
What do you think?
That looks more like CJ to me, Pieanne.

MrP's the one who looks like MrM...
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Ooops, sorry!

Thanx everyone especially Pieanne.

I normally am not confused by punctuation but this sentence here is quite a

challenge for me.