Correct answer: (c) 2 3 1 4
Explanation
- A
2 3 4 1
2 3 4 1 would make silver iodide a rodenticide and zinc phosphide a rain-seeding agent. AgI is the cloud-seeding salt; Zn3P2 is the rodent poison.
- B
2 1 3 4
2 1 3 4 gives eosin the artificial-rain role. Eosin is a red fluorescent dye used in red ink, not in cloud seeding.
- C
2 3 1 4
2 3 1 4 is the match: blue vitriol (copper sulphate) as fungicide, eosin as red ink, silver iodide for artificial rain, zinc phosphide as rodenticide. That is the official key.
- D
2 4 1 3
2 4 1 3 makes eosin a rodenticide and zinc phosphide red ink, which reverses those two uses.
Summary. Official key is (c) 2 3 1 4. CuSO4 is a classic Bordeaux-mixture fungicide; eosin dyes red ink; AgI nuclei seed supercooled clouds; zinc phosphide is a widely used rodent bait. Honour the stored letter (c).