Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. you open the rock and find 31 atoms of argon-40 for every atom of potassium-40. how long ago did the rock form?

We see that in 1 rock, there are 31 atoms of Argon and 1 atom of Potassium so the relative concentration of Potassium is:

1 / 32

or can be written as:

1 / 2^5

So this means that 5 half-lives have passed.

So the years are:

years passed = 5 * 1.25 billion years = 6.25 billion years

if the concentration of products is decreased, the equilibrium will shift toward the products). add an inert gas (one that is not involved in the reaction) to the constant-volume reaction mixture: this will increase the total pressure of the system, but will have no effect on the equilibrium condition.

explanation:

it's c. elements are placed in rows based on how may valencies electrons have.