Four radioactive 10-gram (g) samples with their remaining isotope mass are listed in the table that spans 50 years. Time Americium-241 Californium-249 Silver-108 Mercury-194
10 years 9.84 g 9.80 g 9.84 g 9.85 g
20 years 9.68 g 9.61 g 9.67 g 9.69 g
30 years 9.53 g 9.42 g 9.51 g 9.54 g
40 years 9.38 g 9.24 g 9.36 g 9.39 g
50 years 9.23 g 9.06 g 9.20 g 9.25 g

Which isotope would be expected to have the longest half-life?

A.
Silver-108

B.
Mercury-194

C.
Californium-249

D.
Americium-241