how much of a radioactive kind of yttrium will be left after 20 hours if you start with 720 grams and half-life is 10 hours

180 grams

Step-by-step explanation:

As we know that after each half life, the radioactive substance will become half of the initial.

Given half life of the radioactive yttrium is 10 hours.

So, in 20 hours two half lives will be present.

After first half life, substance will become half of initial,

Initially it was 720 grams, so it will become 360 grams after first half life that is 10 hours.

Now, after second half life, It will again become half of the quantity present after first half life which is 360 grams so it will become 180 grams.

Thus,

After 20 hours only 180 grams of the yttrium will be present.