(c)The speed (v) of electron can be expressed asv=2∈0​hnZe2​….(1) Here,Z = Number of protons in the nucleuse= Magnitude of charge on electron chargen= Principal quantum numberh= Planck's constantIt can be observed from equation (1) that the velocity of electron is inversely proportional to the principal quantum number (n).Therefore, the graph between them must be a rectangular hyperbola.The correct curve is (c).