The given displacement-time graph represents the motion of a simple pendulum immersed in water. This can be determined based on the characteristics of the graph.

A simple pendulum is a mass (usually a bob) attached to a string or rod that swings back and forth under the influence of gravity. When the pendulum is in water, it experiences additional resistance due to the viscosity of the liquid.

In the displacement-time graph, the shape of the graph indicates a periodic motion, which is a characteristic of a pendulum. The graph shows oscillations where the displacement of the pendulum from its equilibrium position changes over time.

If the pendulum was in a vacuum (option 1), there would be no additional resistance, and the graph would have a simpler sinusoidal shape. If the pendulum was in outer space (option 3), there would be no gravity or any other forces acting on it, resulting in a constant displacement rather than oscillations. If it was a point mass moving in air (option 4), the graph would not have the characteristic periodicity of a pendulum and would instead show a different pattern of motion.

Therefore, based on the given characteristics of the graph, option 2, a simple pendulum immersed in water, is the