Correct answer is (a) Standing waves occur when mismatches occurs
Explanation: When there is mismatch, reflections occur and this causes for the occurrence of the standing waves. The standing wave ratio is defined as the maximum voltage to minimum voltage.
\(S=\frac{V_{max}}{V_{min}} =\frac{1+ρ}{1-ρ}\) And reflection coefficient \(ρ=\frac{P_{ref}}{P_{inc}}. \) Therefore S ranges from 1 to infinity.