Of the reactions below, only is not spontaneous. Mg (s) 2HCl (aq) MgCl2 (aq) H2(g) 2Ag (s) 2HNO3 (aq) 2AgNO3 (aq) H2 (g) 2Ni (s) H2SO4 (aq) Ni2SO4 (aq) H2 (g) 2Al (s) 6HBr (aq) 2AlBr3 (aq) 3H2 (g) Zn (s) 2HI (aq) ZnI2(aq) H2 (g)

The answer to the question is

2Ag (s) +2HNO₃ (aq) →2AgNO₃ (aq)+ H₂ (g)

Explanation:

The position of a cell on the reduction potential table determines if a reduction reaction will be spontaneous

The higher the positive reduction potential  the higher the spontaneity of the reduction reaction. that is if the E⁰ cell is positive the cell is a spontaneous voltaic cell, however if the E⁰ cell is negative the cell is a electrolytic non-spontaneous cell

On the standard potential table silver has a low positive potential of

Ag⁺ + e⁻ → Ag = 0.799

It is an oxidizing agent tending to scarcely release electrons, therefore for the reaction to take place, there has to be some external supply of electromotive force.