A citizen may apply for American citizenship after a period of three years. ??
1. The husband or wife of an American citizen may apply for American citizenship after a period of three years.

Is it difference with the sentence below?

2. The husband or wife of an American citizen may apply for American citizenship after a three years period.

Question

A citizen may apply for American citizenship after a period of three years. ??
1. The husband or wife of an American citizen may apply for American citizenship after a period of three years.

Is it difference with the sentence below?

2. The husband or wife of an American citizen may apply for American citizenship after a three years period.

Answer

2 is not right as it stands, but it could be rewritten as "a three year period" (using "year" as an attributive noun). However, I think 1 sounds better still.

Answer

Yes. The second sentence is not grammatically correct. It should be...

2. The husband or wife of an American citizen may apply for American citizenship after a three YEAR period.

Without the final 's' after year.