Astudent calculates the density of an unknown solid. the mass is 10.04 grams, and the volume is 8.21 cubic centimeters. how many significant figures should appear in the final answer?
(1) 1 (3) 3(2) 2 (4) 4

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

Find the number of grams of hcl needed to react completely with .50 moles of magnesium.

Classify this reaction: 2al+n2-> aln.