Apotassium-40 sample starts with 50 atoms, and 1.25 billion years later, there are 25 atoms. what is the half life of potassium-40?

a. 25 years
b. 40 years
c. 1.25 years
d. 2.5 years

Potassium-40 has a half life of 1.25 billion years.

New amount = Original amount × (1/2)^n ; where n is the number of half lives.

Original amount is 50 atoms

New amount is 25 atoms

Therefore;

25 = 50 × (1/2)^n

1/2  = (1/2)^n

Thus; n = 1

n = 1 which is equivalent to 1.25 billion years

Therefore;

Potassium-40 has a half life of 1.25 billion years.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.