Auxin is used by gardeners to prepare weed-free lawns. But no damage is caused to grass as auxin

The correct option is: does not affect mature monocotyledonous plants.

Explanation:

Auxins, particularly synthetic auxins like 2,4-D (2,4-dichlorophenoxyacetic acid), are widely used as selective herbicides in agriculture and gardening.

These synthetic auxins selectively target and kill broad-leaved dicotyledonous weeds. However, they do not affect mature monocotyledonous plants, such as lawn grasses. This selectivity allows gardeners to spray auxin-based weedicides to prepare weed-free lawns without causing any damage to the grass itself.