Question

what is causing this wave?
water molecules in
the tank are
displaced by the
falling drops.
the water drops
travel from left to
right across the
tank.
simulations used in this interactive are by phet interactive simulations
sity of colorado boulder, licensed under cc-by - 4.0 (https://phet.colorado.edu).

Explanation:

When water drops fall into the tank, they displace the water molecules. This displacement causes a disturbance that propagates as a wave. The wave is a result of the energy transfer from the falling drops to the water molecules. The water molecules themselves do not travel across the tank; instead, they oscillate around their equilibrium positions, passing the energy along to neighboring molecules. This is characteristic of a wave, where energy is transferred without the net movement of the medium (in this case, water) over large distances.

Answer:

Water molecules in the tank are displaced by the falling drops.