Explanation

Let's analyze the formation requirements:

1. Two ducks in front of a duck

2. Two ducks behind a duck

3. A duck between two ducks

The smallest number that satisfies all these conditions is *3* ducks in a line:

Duck 1 (front), Duck 2 (middle), Duck 3 (back)

For Duck 2: Duck 1 and Duck 3 satisfy the "two ducks" condition in relation to their positions.

Duck 1 has two ducks (2 and 3) behind it.

Duck 3 has two ducks (1 and 2) in front of it.

Duck 2 is between Duck 1 and Duck 3.