To find<span> the </span>valence electrons in an atom<span>, identify what group the element is in. An element in group 1A has 1 </span>valence electron<span>. For example, Li is in group 1A, so that means it has one </span>valence electron. If the element is in group 2A, then it has two valence electrons<span>.</span>
Answer: one sixteenth
Explanation: Since we know the half life of Cobalt-60 is 5.3 years, and 21.2 years have passed, we can determine how many half lifes have passed by doing division:
21.2 / 5.3 = 4
Since four half lifes have passed, we need to set up the following:
1 / 2^4 (always raise the two to the number of half lifes that have passed, in this case, four have passed, which is what we determined up above!)
When you simplify this you get 1 / 16, which is answer D.
Density=mass/volume so once you find the mass and volume of a substance you can then calculate the density