. A sample of 4 g of cobalt isotope is produced. If the half-life of is 30 years, what will be the mass of the cobalt remaining after 90 years?

Half Life = 90/30 = 3 Half lives

Half Life = 30 years

So,

4 g Cobalt after 30 years = 4/2

=> 2 g

2 g Cobalt after next 30 years = 2/2

=> 1 g

1 g Cobalt after next 30 years = 1/2

=> 0.5 g

So, After 90 years, 0.5g of cobalt isotope will be left.

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.