Question

Actinium-226 has a half-life of 29 hours. If 10g of actinium-226 disintegrates over a period of 145 hours,

Answer 1

Answer: d) 312.5 mg

Explanation:

This problem can be solved using the Radioactive Half Life Formula:

$A=A_{o}.2^{\frac{-t}{h}}$  

Where:

$A$ is the remaining amount of Actinium-226

$A_{o}=10 g$ is the initial amount of Actinium-226

$t=145 h$ is the time elapsed

$h=29 h$ is the half life of Actinium-226

Knowing this, let's find $A$:

$A=(10 g) (2)^{\frac{-145 h}{29 h}}$  

$A=0.3125 g \frac{1000 mg}{1 g}=312.5 mg$