What is the percent composition of carbon in the compound ?

Which of the following statements is true? a. elements in the last period are radioactive. b. atomic weight is the same as atomic mass. c. elements in the same group have the same number of electron shells. d. atomic number equals the number of neutrons in the nucleus of an atom.

What are fossils of organisms that existed over a wide area but only for a limited time period called?

A20 liter cylinder of helium at a pressure of 150 atm and a temperature of 27°c is used to fill a balloon at 1.00 atm and 37°c. what is the volume of the balloon? a. 0.14 liters b. 3000 liters c. 2900 liters d. 2400 liters e. 3100 liters