_CaSO 4 , _O2 +_CaS

1) how many electrons are in each energy level of the following elements? a. he b. na c. na d. ne 2) how many valence electrons are percent in the following atoms? a. s b. mg c. be d. cl 3) which of the following elements are stable as atoms? a. he b. o c. cl d. ar if you are able to provide the work as to how you got the answers that would be greatly appreciated. : )

Fill in the coefficients that will balance the following reaction: a0cr2(so4)3 + a1agno3

How are isotopes of the same chemical element alike? how are they different?