A radioactive isotope has a half-life of 5700. years. Given a 100.0 gram sample of the isotope initially, after a number of years have passed, we find that only 6.250 grams of the original isotope remain.
How many years old is the sample?
a 2.280 x 104 yr
b 1.140 x 104 yr
c 1.710 x 104 yr
d 2.850 x 104 yr

  the mississippians were considered to be  horticulturalists, which means they were

The number of moles of a given mass of a substance can be found without knowing its molecular formula or molar mass. true false

Need what is special about water as a compound? how does water regulate climate? what drives water evaporation?   why is the water vapor fresh water when it rises from the ocean? why might freshwater in the form of snow take longer to enter the water cycle again than liquid precipitation?   what is an aquifer? what role do people play in the water cycle? plz just answer as many as you can ! thx if you !