Which statements best describe half-lives of radioactive isotopes? Check all that apply.
The half-life varies depending on the isotope.
The half-life is the same for every isotope.
Half-lives are always only minutes long.
Half-lives range from fractions of a second to billions of years.
The half-life of a particular isotope is constant.
The half-life of a particular isotope changes constantly.

The half-life varies depending on the isotope.

Half-lives range from fractions of a second to billions of years.

The half-life of a particular isotope is constant.

A and B

Explanation:

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 is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying