Answer: B.) 25% unchanged and 75% stable
Explanation:
Now, to calculate the initial amount of radioactive isotope
[tex]a=\frac{a_o}{2^n}[/tex]
where,
a = amount of reactant left after n-half lives = 60 g
[tex]a_o[/tex] = Initial amount of the reactant = ?
n = number of half lives= 2
Putting values in above equation, we get:
[tex]60=\frac{a^0}{2^2}[/tex]
[tex]a_0=240g[/tex]
Thus percentage of sample unchanged=[tex]\frac{60}{240}\times 100\%=25\%[/tex]
The percentage of sample decayed or has become stable=[tex]\frac{180}{240}\times 100\%= 75\%[/tex]
