Step 1: Identify the parties and subject.
The Farakka arrangement concerns India and Bangladesh over the Ganga/Padma river flows at the Farakka Barrage (West Bengal, near the Bangladesh border).
Step 2: Nature of the agreement.
The dispute was about {sharing river water} during lean months to maintain Kolkata port and downstream needs in Bangladesh. The first formal arrangement was the {1977 Ganges Water Sharing Agreement}; the durable, 30-year {Ganges Water Sharing Treaty} was signed in 1996. Both are river-water sharing instruments tied to Farakka.
Step 3: Eliminate distractors.
It is not a boundary demarcation (B), nor a commercial pact (C), and clearly not “none” (D).
Step 4: Conclude.
\[
\boxed{\text{Farakka Agreement = river water sharing agreement (Option A).}}
\]