To solve this problem, we need to identify the plant hormone used to destroy weeds in a field. Let's analyze each option:$\newline \bullet$IAA (Indole-3-acetic acid):$\newline$ - IAA is a naturally occurring auxin in plants. It is primarily involved in cell elongation, root initiation, and other growth processes.$\newline$ - It is not typically used as a herbicide.$\newline \bullet$NAA (Naphthaleneacetic acid):$\newline$ - NAA is a synthetic auxin used to promote root growth and prevent fruit drop.$\newline$ - It is not commonly used as a herbicide.$\newline \bullet$2, 4-D (2,4-Dichlorophenoxyacetic acid):$\newline$ - 2, 4-D is a synthetic auxin widely used as a selective herbicide.$\newline$ - It is effective in controlling broadleaf weeds in fields without harming grasses.$\newline$ - This makes it the correct choice for destroying weeds.$\newline \bullet$IBA (Indole-3-butyric acid):$\newline$ - IBA is another synthetic auxin used to stimulate root growth in plant cuttings.$\newline$ - It is not used as a herbicide.$\newline$Based on the analysis, the correct option is 2, 4-D, which corresponds to Option 3.