The options of the question is not given so the options are;
(1) Mn(s)
(2) Cu(s)
(3) Ni(s)
(4) Ba(s)
Answer: Mn(s)
Explanation:
The spontaneous reaction depends on the Eo value. The positive Eo value are spontaneous and the negative Eo values are not spontaneous.
so, here the Eo values are:
Eo Zn2+/Zn = -0.763v
Eo Mg2+/Mg = 2.37v
Eo Mn2+/Mn = -1.18v
Therefore, Eo cell (with Zn as one of the half-cell) = Eo Zn2+/Zn - Eo Mn2+/Mn
= -0.763 - (-1.18)
= 0.417v
Whereas, Eo cell (with Mg as one of the half-cell) = Eo Mg2+/Zn - Eo Mn2+/Mn
= -2.37 - (-1.18) = -1.19v
Thus, Mn(s) metal will spontaneously react because it has a positive Eo value and Zn2+(aq), but will not spontaneously react with Mg2+(aq) because it has negative Eo value.
