Final answer:
The pattern for the 2nd harmonic in a pipe open at both ends is N-A-N-A-N, meaning it has a node-antinode-node-antinode-node sequence. Option B is correct.
Step-by-step explanation:
The student's question about the node-antinode pattern for the 2nd harmonic in a pipe open at both ends pertains to the concept of standing waves in physics. For a pipe that is open at both ends, the conditions are symmetrical, meaning it has an antinode at each end.
The first harmonic, or the fundamental frequency, will have one antinode at each end and one node in the middle. For the second harmonic, there will be two nodes between the ends, at one-third and two-thirds of the length of the pipe apart, with antinodes at one-sixth, one-half, and five-sixths of the length. Therefore, the pattern for the 2nd harmonic will look like N-A-N-A-N, where 'N' represents a node and 'A' represents an antinode.