To determine which metal among Pb (lead), Hg (mercury), Na (sodium), and Mg (magnesium) will not spontaneously donate electrons to copper in solution, we can refer to the activity series of metals.
In the activity series, metals that are higher on the list are more reactive and will tend to lose electrons (oxidize) more readily than those that are lower in the series.
From the series provided:
- Pb (lead) is ranked 16
- Hg (mercury) is ranked 20
- Na (sodium) is ranked 6
- Mg (magnesium) is ranked 7
- Cu (copper) is listed at 18
Since copper (Cu) is below lead (Pb), mercury (Hg), sodium (Na), and magnesium (Mg) in the activity series, all of these metals can donate electrons to copper. However, because mercury (Hg) is lower than copper in the activity series, it will not spontaneously donate electrons to copper in solution.
Therefore, the correct answer is:
Hg (mercury)