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)

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.