Concept:Faraday's law of electrolysis relates the mass of a substance deposited to the quantity of electricity passed.Explanation:From Faraday's law, the mass deposited is given by: m=ZQ Here, Z is the electrochemical equivalent and Q is the quantity of electricity. When a graph of m against Q is plotted, the equation is of the form y=mx, where the slope is Z. Therefore, the slope of the graph represents the electrochemical equivalent of the substance.Answer:B. the electrochemical equivalent