Calculate the EMF between copper and silver Ag+e-E=0.89v
Cu=E=0.34v

Depending on the value of , the cell potential would be:

Explanation:

In this galvanic cell, the following two reactions are going on:

Note that the standard reduction potential of ions to is higher than that of ions to . Alternatively, consider the fact that in the metal activity series, copper is more reactive than silver. Either way, the reaction is this cell will be spontaneous (and will generate a positive EMF) only if ions are reduced while is oxidized.

Therefore:

The cell potential is the sum of the electrode potentials at the cathode and at the anode:

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Using data from the 1985 and 2012 CRC Handbook:

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b is the correct

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.