Which metal will spontaneously react with Zn2+ (aq),

but will not spontaneously react with Mg2+

(aq)

according to the activity series

The options of the question is not given so the options are;

(1) Mn(s)

(2) Cu(s)

(3) Ni(s)

(4) Ba(s)

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.