Below are shown, for five metals, reduction reactions and standard electrode potential values. which of these metals is the least reactive?

Above question is incomplete. Complete question is attached below
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Solution:
Reduction potential of metal ions are provided below. Higher the value to reduction potential, greater is the tendency of metal to remain in reduced state.

In present case, reduction potential of Au is maximum, hence it is least prone to undergo oxidation. Hence, it is least reactive.

On other hand, reduction potential of Na is minimum, hence it is most prone to undergo oxidation. Hence, it is most reactive. 

It conforms what ever surface its in.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.