A Concentration Cell Is Constructed by Using the Same Half-Reaction $$E _ { \mathrm { red } } ^ { \circ }$$

A concentration cell is constructed by using the same half-reaction for both the cathode and anode. What is the value of standard cell potential, $$E _ { \mathrm { red } } ^ { \circ }$$ , for a concentration cell that combines a silver anode in contact with 0.10 M silver nitrate and a silver cathode in contact with 0.00003 M silver nitrate? ( $E _ { \mathrm { red } } ^ { \circ }$
= +0.80 V for Ag/Ag⁺)

A) -0.21 V
B) 0.00 V
C) +0.80 V
D) -0.80 V
E) +0.21 V