From the given Prepositions, fill in the blank with the most suitable option :

Sahil has invested a lot of money ________ organic farming.

in

The most suitable preposition to fill in the blank is: in

So, the complete sentence is: "Sahil has invested a lot of money in organic farming."

The correct preposition to use in this context is "in." The phrase "invest in" is commonly used to indicate putting money, effort, or resources into something with the expectation of achieving a benefit or return.