If the half-life of a radioactive material is 8 years, how many years will it take for one-half of the original amount of material to decay?

8 years.

Explanation:

Given data:

Half life of radioactive material = 8 years

Time taken to decay half amount = ?

Solution:

If the half life of an radioactive material is 8 years it means half of its amount will decay in 8 years.

Consider that the original amount of material is 100 g.

At time zero = 100 g

At 1st half life = 100 g/2 = 50 g

Number of half life = T elapsed / Half life

         1    =  T elapsed / 8 years

         1 × 8 years = T elapsed

          T elapsed  = 8 years

SO after 8 years its amount would be remain half.  

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.

they are called fossil fuels