Answer: The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass.
If the initial mass is 185 grams, after the first half-life, the mass will be reduced to 185/2 = 92.5 grams
After the second half-life, the mass will be reduced to 92.5/2 = 46.25 grams
After the third half-life, the mass will be reduced to 46.25/2 = 23.125 grams
So, after three half-lives, there will be 23.125 grams of the isotope left.
It's important to note that the half-life of the isotope is a constant value and it doesn't depend on the initial mass.
Explanation: