Say you have a rock composed entirely of potassium-40. After two half-lives of potassium-40, what fraction of the rock is still composed of potassium-40?

The fraction of the rock that is still composed of potassium-40 is 0.25

Explanation:

To calculate the fraction of the rock that is still composed of K-40, we use the formula:

where,

a = amount of reactant left after n-half lives

= Initial amount of the reactant

n = number of half lives = 2

Putting values in above equation, we get:

Hence, the fraction of the rock that is still composed of potassium-40 is 0.25

your answers are a,b,,e and f

i hope this

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.