Final answer:
After one half-life of 1690 years, half of the 10 grams of radium will have decayed, leaving 5 grams remaining.
Step-by-step explanation:
The question concerns the concept of radioactive half-life, which is the period of time it takes for half of the radioactive atoms in a sample to decay into their daughter elements. In the example given where the half-life of radium (Ra-226) is 1690 years, if you start with 10 grams of radium, after 1690 years you would be left with half of that amount because one half-life will have passed. Therefore, the correct answer is A) 5 grams will be present after 1690 years.