The half-life of radium-226 is 1620 years. Knowing this, you can determine the percentage of an original sample of
Ra-226 that will remain after 4860 years have passed. This percent is?

12.5%

Explanation:

We must first determine the fraction of radium-226 remaining after 4860 years. We can obtain that from;

Nt/No = (1/2)^t/t1/2

Where;

Nt= amount of radium-226 remaining after time t

No= amount of radium-226 available at time t=0

t1/2 = half life of radium-226= 1620 years.

t= time taken for Nt amount of radium-226 to remain= 4860 years

Substituting values;

Nt/No = (1/2)^ 4860/1620

Nt/No = (1/2)^3

Nt/No = 1/8

The percentage of the original sample remaining after 4860 years= 1/8 ×100 = 12.5%

Hence 12.5% of radium-226 remains after 4860 years.

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles

the answer for sodium is 0.186

the answer for rubidium is 0.251