单项选择题
A.Na2Cr2O7·H2OB.Na2Cr2O7·2H2OC.Na2Cr2O7·3H2OD.Na2Cr2O7·4H2O
A.2.6g/cm3B.2.5g/cm3C.2.4g/cm3D.2.2g/cm3
A.Ca(OH)2B.CaOC.CaSO4D.CaCl2