Do the relative proportions of elements in a given compound vary from sample to sample?

How hot is the suns corona? (integrated science)

13. a covalent bond between two atoms is likely to be polar if: a. one of the atoms is much more electronegative than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped molecule. e. one atom is an anion.

Given the following equation: 2a1 + 3mgcl2 --> 2alcl3 + 3mg how many moles of aluminum chloride are produced from 2.5 moles of magnesium chloride?