You start with 4800 grams uranium - 238. It's radioactive and goes through alpha decay. How many grams remain after 7 half-lives.

37.5g

Explanation:

The half-life is the time taken for a radioactive substance to decay to half its original composition;

 Original composition here is  = 4800g  of U-238

How many grams remain after 7 half-lives;

 After each life, the uranium reduces by half;

 Amount remaining  = 4800 x  

                                  = 37.5g

After 7 half lives, 37.5g of the original sample will remain.

1.solid

2.carbon dioxide

3.helium

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.