Why is the average atomic mass used when calculating grams of a substance? A. The number of isotopes in the sample is constantly changing. B. The average atomic mass is known to more significant figures, O C. The elements in the substance are mixtures of their isotopes. D. The exact weights of the isotopes are not known.​

For each of the following types of reactions, write a general reaction formula in the symbolic form—for example, a + b → ab. single-displacement double-displacement synthesis decomposition

1)each group 16 element has how many valence electrons? ( )4 ( )6 ( )8 ( )16 2)how many dots appear in the dot structure for calcium ion, ca2+? ( )zero ( )one ( )two ( )eight 3) which of the following atoms forms a cation to obtain an octet of outer shell electrons? ( )magnesium ( )oxygen ( )fluorine ( )helium 4) an al3+ ion contains 13 protons and 10 electrons. ( )true ( )false 5) valence and non-valence electrons are represented in lewis dot structures. ( )true ( )false

Given sno2 + 2h2 - sn + 2h20 tin oxide reacts with hydrogen to produce tin and water. how many moles of sno2 are needed to produce 500.0 grams of sn?