Explanation:

- Younger leaves show signs of deficiency first: Sulphur deficiency affects new growth, as it is not easily mobilized within the plant.

- High amide and nitrate nitrogen: Sulphur is needed for the incorporation of nitrogen into proteins. Without it, issues arise with nitrogen forms.

- Effect more pronounced on shoots compared to roots and narrow leaf lamina in cruciferous plants: Sulphur is critical for the development of leaves and shoots, with noticeable deficiencies in foliage.

- Blockage of the synthesis of cystine, methionine, etc.: Sulphur is essential for synthesizing amino acids like cystine and methionine.

Option 4: Sulphur is the correct answer.

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