Acertain radioactive element has a half-life of one hour. if you start with 20.0 grams of the element at noon, how much of the radioactive element will be left at 3 p. m.?
a. 10.0 grams b. 5.0 grams c. 2.5 grams d. 1.25 grams

The mass of a neutron is equal to the mass of a proton plus the mass of an electron. true or false false true

1) which of the following is the best example of a physical change? a) sugar dissolving in tea b) firefly glowing 2) in the combustion of ethane, what is/are the reactants? c2h6 + o2 ==> co2 + h2o a) c2h6 and o2 b) co2 and c2h6

650.j is the same amount of energy as? 2720cal1550cal650.cal2.72cal