An isotope, cesium-137, has a half-life of 30 years. Starting with 40 grams, how much is left in 60 years?

You can use a very simple formula for first order decay...

Fraction Remaining (FR) = 0.5n where n is the number of half lives that have elapsed.

In the current problem we want to find the FR, and we know n = 2 half lives elapsed (60 yr/30yr = 2)

FR = 0.52 = 0.25

Since we started with 5.0 g, and we have 0.25 (1/4) left, that would be 5.0 g x 0.25 = 1.25 g

- both b and d.

-since b and d are the closest coastlines then that makes it the most affected.

< 3

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.