The unit of resistance is MCQ with Answer and Explanation

Explanation:
Superconductivity occurs in certain materials below a critical temperature T_c, where electrical resistance drops abruptly to zero, and magnetic fields are expelled (Meissner effect). Option B describes insulators; C and D are unrelated. Memory aid: 'Superconductor: R=0 below T_c; perfect diamagnetism'. This modern physics concept is frequently tested in competitive exams. Always distinguish superconductivity (zero resistance) from perfect conductivity (theoretical limit); real superconductors exhibit Meissner effect, a defining property.

Explanation:
Left hand rule for motor effect (force). Right hand for generator.

Explanation:
Diffraction (bending around obstacles) is wave phenomenon explained by Huygens' principle. Particle model predicts straight-line propagation. Memory aid: 'Diffraction/interference ⇒ wave nature; photoelectric ⇒ particle nature'. Wave-particle duality frequently tested in competitive exams.