The order of ease of reduction of H+1, Cu+2 and Ag+1:

Explanation

The more positive the standard electrode potential, the more readily the ion accepts electrons, and the values are plus 0.80 V for silver, plus 0.34 V for copper and zero for hydrogen by definition. Silver is therefore reduced most easily and hydrogen least, which is also why copper and silver do not displace hydrogen from dilute acids. Note that options (a) and (d) were printed identically in the original paper.