Answer:
+3
Explanation:
Chlorine is anion with a -1 charge. But they are three chlorine atoms.
-1 * 3 = -3
So they have a -3 charge.
So to balance the compound, the nickel has to be a cation with a +3 charge.
-3 + 3 = 0
Furthermore, a chemical bond always has a 0 charge. Remember that.
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Answer:
Only
gives spontaneous reaction.
Explanation:
A redox reaction will be spontaneous if standard reduction potential (
) of the reaction is positive. Because it leads to negative standard gibbs free energy change (
), which is a thermodynamic condition for spontaneity of a reaction.

Where
and
represents standard reduction potential of reduction half cell and standard reduction potential of oxidation half cell.
(1) Oxidation:
; 
Reduction:
; 
So, 
Hence this pair will give spontaneous reaction.
(2) Similarly as above, 
Hence this pair will give non-spontaneous reaction.
(3) Similarly as above, 
Hence this pair will give non-spontaneous reaction.
(4) Similarly as above, 
Hence this pair will give non-spontaneous reaction.
Answer:
molecules, elements
Explanation:
molecules are a mix of elements