Which point defect in its crystal units alters the density of a solid? please please answer ​

What sources of error may have contributed to the percent yield not being 100 percent? think about things that may have led to inaccurate measurements or where mass of the product could have been lost if this experiment was conducted in a physical laboratory.

4al + 3o2 → 2al2o3 what does the "3" in front of o2 stand for? a) it indicates that there are 5 oxygen atoms after you add the coefficient and the subscript. b) it indicates that that there are are total of 6 oxygen atoms all bonded together as a single molecule. c) it indicates that there are 3 oxygen molecules chemically bonded to each other in the reaction. d) it indicates that there are 3 separate oxygen molecules in the reaction.

What is true according to the second law of thermodynamics