Answer:
3.9 billion years
Explanation:
The half-life of potassium-40 is the time it takes for half of it to decay.
After one half-life, half of the original amount will remain.
After a second half-life, half of that amount will remain, and so on.
We can construct a table as follows:

We see that the mass will drop to 10 g after three half-lives.
1 half-life = 1.3 billion years
3 half-lives = 3.9 billion years
The correct answer is: daughter cells will have abnormal chromosome numbers and this condition is called aneuploidy.
Nondisjunction is the failure of homologous chromosomes (or sister chromatids) to separate during the process of cell division and consequently lead to aneuploidy. There are three forms of nondisjunction:
• Nondisjunction in meiosis I (pair of homologous chromosomes unable to separate in meiosis I),
• Nondisjunction in meiosis I (sister chromatids unable to separate during meiosis II), and
• Nondisjunction in mitosis (failure of sister chromatids to separate during mitosis)