How many electrons are found in a C and O2-, respectively?

Carbon has a total of six electrons and there are a total of ten electrons in the oxygen ion.

What we can easily find in common with carbon and oxygen atom is the fact that the both of them have two shells. We can also refer to these shells as energy levels.

In both atoms, the first shell contains only two electrons. For carbon, the second shell contains four electrons while the second shell of oxygen ion contains eight electrons.

Hence, Oxygen ion has two electrons in the first shell and eight electrons in the second shell(total of ten electrons) while carbon has two electrons in the first shell and four electrons in the second shell (a total of six electrons).

The electronic configuration of carbon is: 1s2, 2s2, 2p2

The electronic configuration of oxygen ion  is: 1s2, 2s2, 2p6

Learn more: link

first, consult an activity series chart to determine if al is more reactive than fe. it is, so it will replace the fe. now, one can continue with the problem.

next, make sure you have a correctly balanced equation.

3feo + 2al ==> 3fe + al2o3

now, determine which reactant (feo or al) is in limiting supply.

moles feo present = 125 g x 1 mole/71.8 g = 1.74 moles

moles al present = 25.0 g x 1 mole/26.98 g = 0.927 moles

since from the balanced equation, it take 3 mol feo for every 2 mol al, al will be limiting.

you can determine this simply by dividing moles of each by their coefficient in the balanced equation. for example: 1.74/3 = 0.58 and 0.927/2 = 0.464. al is less, so it is limiting.

finally, using the stoichiometry in the balanced eq. determine mass of fe that can be produced from 0.927 moles of al.

0.927 moles al x 3 moles fe/2 moles al x 55.8 g/mole = 77.6 g

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !