How was the nobility of russia formalized by peter the great and later catherine the great?

The Russian nobles didn't enjoy the privileges and dignity the European nobles used to enjoy. Peter the Great introduced some reforms which formalized the nobility of Russia. He ennobled the new comers and reduced the influence of Boyars, Russia's elites. He introduced the table of ranks - a set of 14 ranks applied to civil services and military as well. Anyone who attained at least the 8th rank was ennobled.The nobles were educated, westernized and bureaucratized.  

Catherine the Great also took some measures with regard to nobility. She realized the dependence on nobility and thus She gave them more control over their lands and serfs. Further The 1785 charter to nobility established them as a separate estate and assured their privileges and dignity.

yup! you are correct it is b.

b - those executed came from every social and economic class