4cr+3o2-> 2cr2o3
how many moles of o2 react with 4.55 moles of cr?

3.4125 mole O₂

Explanation:

Data Given:

Mole of Cr = 4.55 mole

Mole of O₂ = to be calculated

             4Cr + 3O₂> 2Cr₂O₃

from the above reaction data obtained:

               4Cr     +     3O₂   >  2Cr₂O₃

               4mole       3mole                  2moles

The above reaction show that

4 mole of the Cr combine with 3 mole of O₂ and produce 2 moles of Cr₂O₃

in other words

                    4 mole of the Cr ≅ 3 mole of O₂

apply the unity formula

                     4 mole of the Cr ≅ 3 mole of O₂

                      4.55 mole of the Cr ≅  X mole of O₂

so by cross multiplication

              4 mole of Cr x  X mole of O₂ ≅ 3 mole of O₂ x 4.55 mole of the Cr

we have to find moles of O₂ so by rearrangement of the above equation

 X mole of O₂ =  3 mole x 4.55 mole

                                   4 mole

X mole of O₂ = 3.4125 mole

So

4.55 mole of Cr will react with 3.4125 mole O₂

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)