The correct choice is (c) ΔE/Δi=[βa*βb]/[2.3*icorr*(βa+βb)]
To elaborate: The slope of linear polarization curve is determined by using ΔE/Δi=[βa*βb]/[2.3*icorr*(βa+βb)] where βa , βb are Tafel slopes of anodic and cathodic reactions and icorr is the current density at the intersection point of anodic and cathodic reaction.