Name a hormone which:
$(A)$ is gaseous in nature
$(B)$ is responsible for phototropism
$(C)$ induces femaleness in flowers of cucumber
$(D)$ is used for killing weeds (dicots)
$(E)$ induces flowering in long day plants

(A-ETHYLENE, B-AUXIN, C-ETHYLENE, D-2,4-D, E-GIBBERELLINS) Ethylene is a plant hormone that exists in a gaseous state at room temperature.
$(B)$ Auxin is primarily responsible for phototropism,as it promotes cell elongation on the shaded side of the stem.
$(C)$ Ethylene promotes the development of female flowers in cucumber plants,thereby increasing the yield.
$(D)$ Synthetic auxins,such as $2,4-D$ ($2,4-dichlorophenoxyacetic$ acid),are used as herbicides to selectively kill broad-leaved dicot weeds.
$(E)$ Gibberellins are known to induce flowering in many long-day plants,especially under non-inductive conditions.