WILL GIVE BRAINLIEST

4. For A it's 0.6×10^9 years as that's when the mass percent reached 50%.

For B it's 4.5 × 10^9 years as that's when mass% reached 50%.

For C it's 13 × 10^9 years.

For D it's not visible on the graph. But it'll take at least another 14 × 10^9 years to reach half life.

5. A has the shortest half life since it took it less time to deplete to half of it's original mass percent.

6. A is unstable because it has the shortest half life and this means it'll take it very fast to decay.

C. Adding a catalyst

Explanation:

Because the catalyst increases the rate of chemical reaction