The idea that social and economic inequalities must be to the greatest benefit of the least-advantaged members of society is called:

capitalism.
communism.
socialism.
the difference principle.

socialism?

You need to look up each of those terms.

http://www.dictionary.com

i said socialism

communism.

The correct answer is the difference principle. The idea that social and economic inequalities must be to the greatest benefit of the least-advantaged members of society is known as the difference principle. It is a concept developed by the political philosopher John Rawls as part of his theory of justice.