Answer:
Correct answer is B
Explanation
In a standing wave, node is a point where amplitude of the wave is minimum or zero. For example, in a guitar in which string vibrates, the ends of the string are known as nodes. In this question at point B amplitude of the wave is minimum (approximately zero). Therefore in this figure point B is node. And the point where the amplitude of the wave is maximum is known as anti-node. antinodes occur midway between the nodes. In given figure at point A amplitude is maximum, therefore point A is anti node.