Which half reaction is most easily reduced?
ag+ + e− → ag = 0.80 v
br2 + 2e− → 2br− = 1.07 v
fe3+ + e− → fe2+ = 0.77 v
zn2+ + 2e− → zn = –0.76 v

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.