Final answer:
The wavelength of the standing wave in a string with five antinodes is L/2 because each antinode corresponds to half a wavelength and five antinodes imply the string accommodates five half-wavelengths, therefore the wavelength equals the string's length (L) divided by 2.
Step-by-step explanation:
The wavelength of the standing wave in a string with five antinodes is L/2. In a standing wave on a string that is fixed at both ends, there is a node at each end of the string. Considering five antinodes, there would also be six nodes in total, as each antinode is flanked by two nodes, except at the ends of the strings where the end nodes are single. The pattern would be Node-Antinode-Node, repeated five times. Since there are five complete half-wavelengths (since each node to node or antinode to antinode is half a wavelength), the total wavelength for the five antinodes would be the string's length (L) which contains five half-wavelengths. Therefore, the wavelength (λ) is twice the length of one of these segments, giving a wavelength of λ = L/2. This matches option A, which states that the wavelength is L; however, remembering that one antinode is equivalent to half a wavelength, for a string with five antinodes, the correct answer would be the string's length divided by 2, L/2, which is not explicitly provided in the options given.