The half-life of tritium or hydrogen-3 is it 12.32 years, after about 24.6 years how much of a sample of tritium remain unchanged?
a 1/3
b 1/2
c 1/8
d 1/4

The answer will be D, 1/4.

How you come to this conclusion( for future reference to anyone stuck on this ), is figure out how many half-lives have passed. In this case two half-lives have passed ( 24.6 is 12.32 + 12.32 ), so just put into your calculator 1/2 x 1/2 ( or .5 x .5 ). Make sure your answer is in fraction form, and you have your answer! Hope this helps any who may see this!

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.