Answer:
See explanation
Step-by-step explanation:
Mass of samarium-151 originally present (No) = 5 g
Mass of samarium-151 discovered (N) = 0.625 grams
time taken = ?
half life of samarium-151 (t1/2) = 96.6 years
From
N/No = (1/2)^t/t1/2
0.625/5 = (1/2)^t/96
0.125 = (1/2)^t/96
1/8 = (1/2)^t/96
(1/2)^3 = (1/2)^t/96
3 = t/96
t = 3 * 96
t = 288 years
The mass of europium-151 when the rock was discovered is obtained from;
Fraction of samarium-151 left = 1/8
Fraction of europium-151 formed = 1 - 1/8 = 7/8
Mass of europium-151 = 7/8 * 5 = 4.375 g
