To prepare a weed-free lawn, gardeners extensively use a specific plant growth regulator that selectively kills dicotyledonous weeds but does not affect mature monocotyledonous plants. Identify this plant growth regulator from the given options.

Step-by-step solution

2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin that is widely used as a herbicide. It selectively kills broad-leaved, dicotyledonous weeds but does not affect mature monocotyledonous plants. Because of this property, it is extensively used by gardeners to prepare weed-free lawns. Answer: 2,4-D