Answer:
Any two metal which are not ductile are iron and zinc ..
I would say B because c and d would decrease competition and a would do the same, or just kill the ecosystem.
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I think it is Sodium,hypochlorite
Answer:
The coefficient tells you how many molecules of that substance there is. The subscript tells you what the substance it. It tells you the the amount of each element there are in the molecule. Changing it would change the substance itself.