Question

Many groups experience polarization, which is when opinions become more and more extreme.

Answer 1

True, group polarization is when the dominant attitude of a group becomes stronger and stronger.

Answer 2

Many groups experience polarization, which is when opinions become more and more extreme.The statement is TRUE.
Polarization is the tendency for the dominant attitude of a group to become stronger or extreme. 
For instance, when a discussion concerning racism, members of the cluster who are racist can defend their views way more aggressively than they'd have before.