How many moles of water are needed to react to produce 5.0 moles of sodium hydroxide? Please help!!!

If 1.63 times 10 negative 4 of helium dissolves in 100.0g of water, what is the concentration in parts per million

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 happened in 2012 and how does it illustrate the importance of understanding the sun and how it works?