The first step for these types of problems is to fix the stoichiometry.
1. You can see that you need two NO3 molecules in the reagents because there are two in the products. To do this, simply add a 2 in front of the AgNO3. This creates 2Ag in the products. So now you have:
Cu + 2AgNO3 --> Cu(NO3)2 + 2Ag and you can see that the ratio of copper to silver is 1:2
Follow this same pattern for the rest of the reactions:
2. 2KClO3 --> 2KCl + 3O2 (because you need to fix the amount of oxygens to be equal in both the products and reactants). So the ratio of oxygen to potassium chlorate is 3:2 (although you might want to specify with your professor if he/she means oxygen molecules or the element oxygen, because if he/she means element oxygen it would be 6:2, or 3:1)
3. N2 + 3H2 --> 2NH3 (because you have to even out the number of nitrogens and hydrogens in the products and reactants), so the ratio of nitrogen to ammonia is 1:2 (again, specify if he/she means the molecule nitrogen or the element nitrogen to make sure this is correct)
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