<prompt> Roentgen is a unit of-RadioactivityRadiation exposureAbsorbed doseDose equivalent  <response>: Ans is b i.e. Radiation exposure Old unit of radiation exposure is Roentegn and new unit SI is ColumbcmQuantity measuredOld unitNew SIunit RadioactivityCurieBecquerel1 curie 3.7 x 101 becquerel -2.7 x 10Radiation exposureRoentgenColumbcm Absorbed doseRadGray100 rad 1 gray1 rad 0.01 grayDose equivalentRemSievert Sv100 rem 1 SvIrem 0.01 Sv 