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.
Physical or mental traits change
It's letter C. When ever you read "breaks down" always think decomposition. When you read that compound get together to form "a single" compound, think synthesis.
Answer:
C. physical
Explanation:
A mixture is a physical combination. Mixtures are combinations of compounds and molecules without any chemical reaction taking place.
Mixtures have the following properties:
- They have an indefinite composition i.e they consist of two or more elements and or compounds in any proportion by mass
- Their constituents retains their identities i. e physical property is retained.
- Their constituents reacts differently to changed conditions.
- They are easily separated into constituents by physical methods
