Correct Answer: London theory

Solution : The correct answer is the London theory .

London theory was the first phenomenological explanation of superconductivity. It was proposed in 1935, not long after the brothers Fritz and Heinz London learned that superconductors emit magnetic fields. The Meissner effect, wherein a material exponentially expels all internal magnetic fields when it reaches the superconducting threshold, may be explained by the equations of this theory, which is a significant achievement.