Question

A 6.95 gram sample of a radioactive substance has a half-life of 58 min. How much substance is left after 1 hours and 56 minutes?

• A. 0.869 grams
• B. 0.434 grams
• C. 3.48 grams
• D. 10.43 grams
• E. 1.74 grams

Answer 1

Answer: (E)

1.74 grams

Given : $T_{1/2}=58$ min $t=1$ hr and $56$ min $=116$ min

Amount of substance present initially, $R_o=6.95$ gram

Remaining amount, $R=\frac{R_o}{2^n}$ where, $n=\frac{t}{T_{1/2}}$

$\therefore$ $n=\frac{116}{58}=2$

Thus remaining amount, $R=\frac{6.95}{2^2}=1.74$ gram