A sample contains 10.5 g of the radioisotope Pb-212 and 157.5 g of its daughter isotope, Bi-212. How many half-lives have
passed since the sample originally formed?

The sample have passed 4 half lives after the sample was originally formed.

Explanation:

Half life is the time required to calculate the amount of a sample to half its value.

To calculate number of half- lives , the equation is used

(1/2)^n =x

where, n is  number of half -lives

              x is the remained fraction of a sample

we have to find n, so we can do it by calculating x. if sample contains 10.5 g of the radioisotope pb-212 and 157.5 g of daughter isotope

then the total is

157.5 g + 10.5 g = 168 g of the sample

Out of this 168 g, 10.5 g remained of the radioisotope pb-212.

The fraction is

10.5 ÷ 168 = 0.0625

x = 0.0625

(1/2)^n = x

n * log (1/2) = log (x)

n * log (0.5) = log (x)

n =

n =

n =

n= 4

Thus, the number of half lives is 4

the answer would be a

conduction is the transfer of thermal energy (heat in transfer) due to collisions between the molecules in the object. collisions between adjacent atoms and molecules transfer kinetic energy from the warmer to the cooler object. the objects must be in physical contact.