Q.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 is the gaseous plant hormone.

b. Auxin is responsible for phototropism — it was through Darwin's observations of coleoptiles bending toward light that its existence was first inferred, later isolated by F. W. Went from coleoptile tips.

c. Ethylene induces femaleness in the flowers of cucumber, increasing yield.

d. 2,4-D (a synthetic auxin) is used for killing dicot weeds, since it does not affect mature monocots, and is used to prepare weed-free lawns. …

a. Gaseous hormone. Ethylene is the plant growth regulator that is gaseous in nature, synthesised in large amounts by tissues undergoing senescence and by ripening fruit.

b. Hormone responsible for phototropism. Auxin is responsible for phototropism. It was through Charles and Francis Darwin's observations of canary-grass coleoptiles bending toward unilateral light that the existence of a transmittable growth influence from the coleoptile tip was first established, and this substance was later isolated as auxin by F. W. Went.

c. Hormone that induces femaleness in cucumber flowers. Ethylene induces femaleness in the flowers of cucumbers, and this effect is used commercially to increase the number of female flowers and hence the crop's yield.

d. Hormone used for killing dicot weeds. 2,4-D, a synthetic auxin, is used as a herbicide to kill dicotyledonous weeds; because it does not affect mature monocotyledonous plants, it is used specifically to prepare weed-free lawns. …

Method: Matching a Described Effect to Its Hormone

Use this method for any "name a hormone which does X" list question covering several distinct, unrelated effects.

Steps

Step 1: Treat each part as an independent match, not a themed set

Each sub-part describes a different, specific physiological effect — resist the urge to assume they're all testing the same hormone; go through the list of the five classical PGRs (auxin, gibberellin, cytokinin, ABA, ethylene) and check each part against their defining properties individually.

Step 2: Use the DEFINING, most specific property for each match, not a loosely related one

Match physical state (gaseous) to ethylene; a growth-toward-light response (phototropism) to auxin, since it is the classic hormone shown to mediate directional light-driven growth; sex-expression changes in cucurbits to ethylene; herbicidal dicot-selective killing to 2,4-D specifically (not auxin broadly); substituting for a long-day photoperiod requirement to gibberellin.

Step 3: Distinguish auxin in general from a NAMED synthetic auxin when the question is specific …