According to reference table adv-10, which reaction will take place spontaneously? 1.  ni2+ +pb(s) → ni(s) + pb2+ 2.  au3+ + al(s) → au(s) + al3+ 3.  sr2+ + sn(s) → sr(s) + sn2+ 4.  fe2+ + cu(s) → fe(s) + cu2+

Missing table

http://www.chemeddl.org/services/moodle/media/QBank/GenChem/Tables/EStandardTable.htm

Ni2+ +Pb(s) → Ni(s) + Pb2+
The potential of the oxidation of Pb(s) --> Pb2+(aq) is 0.126 V 
The potential of the reduction go Ni2+(aq) --> Ni(s) is -0.25 V 

Add the two together and the potential for the reaction is -0.124 V (NO SPONTANEOUS THE SIGN IS NEGATIVE)

au3+ + al(s) → au(s) + al3+Au3+(aq) ->   Au(s)  +1.5 VAl -> Al3+  +1.66VV= 3.16 (SPONTANEOUS THE SIGN OF THE PONTENTIAL IS POSITIVE)Sr2+ + Sn(s) → Sr(s) + Sn2+

Sr2+(aq) + 2 e–    Sr(s)  V= -2.89V
Sn -> Sn2+ V= 0.14 V
V= -2.75 V (no spontaneous)

Fe2+ + Cu(s) → Fe(s) + Cu2+
Fe2+(aq) + 2 e–    Fe(s)  V= -0.44 V
Cu -> C2+  V = - 0.337V

V= - 0.777V (no spontaneous)

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.