i have to answer the questions in the link above 1-20 as an extra credit assignment..pleaseee help???? :?

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Those questions each have to do with balancing a chemical equation. We can look at question number 1 as an example of how to complete the remaining questions:

____Al   +    ____S     ---------->  ____Al2S3


To balance a chemical equation like the above is easy; just ask the question, "How many Al atoms do I need, and how many Sulfur atoms do I need?" The '2' after the Al means that you end up with two Al atoms. Likewise, the '3' after the 'S' means that you end up with 3 sulfur atoms for every two aluminum atoms. So your answer is:

__2__Al   +    __3__S     ---------->  __1__Al2S3


What if you have more atoms on one side than the other? Then increase the number of atoms produced. For example,

____Zn    +    ____O2    ---------->  ____ZnO


ZnO only has 1 oxygen, but the reaction is with O2, which has two oxygens. So, increase the number of ZnO molecules to 2:

____Zn    +    ____O2    ---------->  __2__ZnO

Now, perform the same operation as in the first example: you need 2 Zn atoms, and 2 O atoms:

__2__Zn    +    __1__O2    ---------->  __2__ZnO

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