The description you have provided does not correspond to a study called the “Belmont study”. The one I can find is The Belmont Report (1979) which is an ethical guideline document produced by the US National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research. It outlines ethical principles such as respect for persons, beneficence and justice, and is not an empirical study on group polarisation.
Location: 1.3 Social Science & Socio-Cultural Psychiatry Quiz