Determine which of the following pairs of reactants will result in a spontaneous reaction at 25°C.

a) Zn(s) + K⁺(aq)
b) Fe(s) + Ba²⁺(aq)
c) Cr³⁺(aq) + Pb(s)
d) Sn4+(aq) + Mn(s)
e) None of the above pairs will react spontaneously.