Select the correct answer. A sample taken from a layer of mica in a canyon has 2.10 grams of potassium-40. A test reveals it to be 2.6 billion years old. How much
potassium-40 was in the sample originally if the half-life of potassium-40 is 1.3 billion years?
O A.
4.20 g
O B.
8.40 g
O C.
12.6 g
• D.
16.8 g
O E.
25.2 g

8.36 g

Explanation:

From;

0.693/t1/2 = 2.303/t log (No/N)

t1/2 = half life of potassium-40

t = age of the sample

No= initial amount of the sample

N= amount of the sample at time t

Substituting values;

0.693/1.3 × 10^9 = 2.303/2.6 × 10^9 log (No/2.10)

5.33 × 10^-10 = 8.86 × 10^-10 log (No/2.10)

5.33 × 10^-10/8.86 × 10^-10 = log (No/2.10)

0.6 = log (No/2.10)

Antilog (0.6) = (No/2.10)

No = 2.10 × Antilog (0.6)

No= 8.36 g

yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes

explanation:

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e