To calculate the corrosion current density, we can use the following equation:Corrosion current density i_corr = Corrosion current I_corr / Area A First, we need to find the corrosion current I_corr . We can do this using Ohm's Law:Corrosion current I_corr = Voltage V / Polarization resistance R_p However, we don't have the voltage V directly given in the problem. Instead, we can use the Tafel equation to find the voltage:V = -b * log i_corr where b is the Tafel slope, which is typically around 0.12 V/decade for silver in NaCl solutions.Now we have two equations with two unknowns V and i_corr . We can solve these equations simultaneously to find the corrosion current density.1. V = -b * log i_corr 2. I_corr = V / R_pSubstitute equation 1 into equation 2:I_corr = -b * log i_corr / R_pNow we can plug in the given values:I_corr = -0.12 * log i_corr / 125To solve this equation, we can use an iterative approach or numerical methods. Using a numerical solver, we find that:I_corr 9.6 10^-6 ANow we can find the corrosion current density:i_corr = I_corr / Ai_corr = 9.6 10^-6 A / 20 cm i_corr 4.8 10^-7 A/cmSo, the corrosion current density of the silver electrode in a 0.5M aqueous solution of NaCl at 25C is approximately 4.8 10^-7 A/cm.