Question

which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?

Answer 1

The right answer is polar group attract another one.

Amphipathic, amphiphilic and amphipolar, synonymous terms, denote a molecule (usually organic) carrying both a hydrophilic group (able to bind to water) and a hydrophobic group ("who does not like water").

These molecules are surfactants, in that they modify the surface tension between two media. The active components of detergents and soaps are amphipathic molecules, whose double solubility is exploited, in water (thanks to hydrophilic groups) and in fatty media (thanks to hydrophobic groups).

The membranes of living cells are made of two layers of molecules of this type (phospholipids).

Answer 2

The statement must be mentioned in explaining why amphipathic molecules line up at a water surface is polar group attract one another.

Amphipathic molecule are those which have both polar and non-polar part. Example phospholipids have both polar and non-polar parts  that is non-polar fatty acid tail and polar head.

Polar water molecule pull together , holding the polar parts of the amphipatic molecule and squeezing out the non-polar parts .That leave the non-polar parts in air .