Question

A radioactive substance has a half-life of 5 million years. What is the age of a rock in which 25% of the original radioactive atoms remain

Answer 1

10 million years

Answer 2

d. 10 million years

Step-by-step explanation:

These are the options for the question

Choose one answer.

a. 2.5 million years

b. 5 million years

c. 15 million years

d. 10 million years

✓half-life of the radioactive substance= 5 million years

✓ Then for every 5 million years, original radioactive given (100%) percentage is reduced by factor of 1/2.

✓ 1st 5 million year; After the first 5 million years, the original radioactive is reduced as;

(100%) × 1/2 = 50% remains

✓2nd 5 million year: At 10 millions year, the 50% remaining radioactive is reduced by factor of 1/2

(50%) × 1/2 = 25% remains

Hence, at At 10 millions years 25% of the original radioactive atoms remain

.