Uranium-235 (U-235) has a half-life of around 700 million years. U-235 will decay into (after a series of separate decays) Pb-206 (Lead-206). A rock sample is found to have 6.25% (1/16) of its original U-235. a.) How many half-lives have passed?

b.) How many years has this taken?

c.) If there were 30 grams of U-235 originally, how many grams would be left now?

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.

i think its 5049.

i hope this !

they are all solids.