Question

After three half-lives, a sample contains 20 grams of parent isotopes. How many grams of the parent isotope were present to start? 320 160 80 40

Answer 1

`\huge\boxed{\sf 160\ g}`

Step-by-step explanation:

Half-life:

• The period of time in which a sample becomes half of its original amount is known as half life.

Here,

Half life = 3

Sample Amount left = 20 g

Before 3rd half-life:

= 20 × 2

= 40 g

Before 2nd half-life:

= 40 × 2

= 80 g

Before 1st half-life:

= 80 × 2

= 160 g

So, the initial amount of sample was 160 grams.

`\rule[225]{225}{2}`