Answer:
In Cl
, the 2 is a subscript because it indicates there are 2 of the same elements. The Lewis structure would display it as Cl-Cl.
On the other hand, a superscript would indicate a specific charge.
All subscripts show the amount of the specific element there is.
An example would be O
or N, they both show that there are 2 of the same elements.
If the subscript is outside a parenthesis such as 
it indicates there are 2 
molecules.
To find average atomic mass, multiply each isotope's atomic mass with its relative abundance and add it all up.
15.012*0.1423 + 16.988*0.3348 + 19.177*0.5229 = 17.851 (5 s.f.)
The answer is A. An electrolytic cell is by definition a non-spontaneous chemical reaction that uses something like a battery to power it. The spontaneous counterpart is the voltaic cell.
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To convert 790 calories to joules
3305.36 joules
