Chemistry and Chemical Reactivity (9th Edition)

$4.33\ mg$
For a first-order process: $ln(C/C_0)=-kt;\ k=0.693/t_{1/2}$ For constant volume, we can use the equation on a mass basis. $ln (m/5.6\ mg)=-0.693/2.7\ d\times 1.0 \ d=4.33\ mg$