Radioactive Radium ${ } ^ { 226 } \mathrm { R }$

Multiple Choice

Radioactive radium, ${ } ^ { 226 } \mathrm { R }$ , has a half-life of 1620 years. If you start with 5.00 grams of the isotope, how much will remain after 1000 years? Round your answer to two decimal places.

A) 1.91 grams
B) 4.74 grams
C) 5.00 grams
D) 2.70 grams
E) 6.00 grams