There is a 30 g sample of Be-11. It has a half-life of about 14 seconds. How much will be left after 28 seconds?A.3.75 gB.7.5 gC.15 gD.30 g

After 28 sec 7.5 grams of Be will be left

Explanation:

Given data:

Total amount of Be = 30 g

Half life of Be = 14 sec

Mass left after 28 sec = ?

Solution:

First of all we will calculate the number of half lives in 28 sec.

Number of half lives = T elapsed / half life

Number of half lives = 28 sec / 14 sec

Number of half lives = 2

AT time zero = 30 g

At first half life = 30 g/2 = 15 g

At second half life = 15 g/ 2 = 7.5 g

So after 28 sec 7.5 grams of Be will be left.