Which of the following has greatest reducing power?

Which of the following has a higher reducing power?

Which of the following has the highest reducing power?

Which of the following has largest protecting power -

Given : E_(Li^(+)|Li)^(@)=-3.05V, E_(Mg^(2+)|Mg)=-2.36V, E_(Ba^(2+)|Ba)^(@)=-2.90V and E_(Na^(+)|Na)^(@)=-2.17V at 25^(@)C . Which one of the following ions has the greatest reducing power -