Correct Answer: Lucrative

Solution : The first option is correct.

The option that can be used as a one-word substitute for the given group of words is lucrative.

Explanation:

Lucrative: It is an adjective that specifically describes something that is profitable or produces financial gain.
Ludicrous: It means absurd or ridiculous, and it does not convey the idea of financial gain.
Luddite: It refers to a person opposed to technological change and is unrelated to financial gain.
Lugger: It refers to a type of fishing boat and is not associated with financial profitability.

Therefore, lucrative is the most appropriate one-word substitute for the given group of words.