Based on the activity series, magnesium will spontaneously react with zinc chloride, so the two reactants that react spontaneously are Mg(s) and ZnCl2(aq).
When considering spontaneous reactions based on Reference Table J, it is important to use the activity series of metals to determine which reactions will occur without an external energy source. In this context, looking at the option of Mg(s) + ZnCl2(aq), magnesium is higher in the activity series than zinc, which means that magnesium can displace zinc from its compound, resulting in a spontaneous reaction. For this reason, out of the given choices, Option 1: Mg(s) + ZnCl2(aq) will react spontaneously. This can be deduced using the information that a metal can displace a less reactive metal from its compound, as illustrated in the examples where zinc displaces copper and iron displaces copper from their respective compounds.