Half Life

Step 1: Understanding the decay process.
The number of nuclei left after a certain time in a radioactive decay process is given by the formula: where: - is the number of nuclei remaining after time , - is the initial number of nuclei, - is the half-life of the substance.

Step 2: Substituting the values.
Here, , minutes, and minutes. Substituting into the formula:

Step 3: Conclusion.
The correct answer is (B) 128.