Answer: A. Industrial hydrogen for ammonia synthesis is produced by steam reforming of hydrocarbons — usually natural gas (methane): \(\text{CH}_4 + \text{H}_2\text{O} \rightarrow \text{CO} + 3\text{H}_2\). This is a form of cracking and is the dominant source of industrial \(\text{H}_2\) worldwide.
B (electrolysis of NaOH) is technically possible but uses far more electricity per kilogram of \(\text{H}_2\) than steam reforming — not the standard industrial source.
C (extraction from air) is wrong: dry air contains essentially no free hydrogen; what's there is trace.
D (Group I metal + water) gives \(\text{H}_2\) but Group I metals themselves are extracted by electrolysis of their molten salts — net energy cost is enormous and the reaction is dangerous. Industrially impractical.
Cracking of hydrocarbons is the answer: A.
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