Question

A 6.95 gram sample of radioactive nobelium-259 has a half-life of 58 min. How much is left after 2 hours and 54 minutes?

• A. 0.869 grams
• B. 0..434 grams
• C. 3.48 grams
• D. 10.43 grams
• E. 1.74 grams

Answer 1

The correct option is A 0.869 grams

Total time is 2 hours and 54 minutes, i.e., $2\times 60+54=174$ minutes.
The half life period is 58 minutes.
The number of half life periods $=\frac{174}{58}=3$.
After 2 hours and 54 minutes, the amount left is $\frac{6.95}{2^3}=0.869$ g.