3)
Atoms of which two elements have a combined total of 23 protons?
A) Sodium, Na, and magnesium, Mg
B) Boron, B, and carbon, C
C) Copper, Cu, and zinc, Zn
D) None of these

Option A is correct. The atoms of which two elements have a combined total of 23 protons are Sodium and magnesium

The proton of an element is also known as its atomic number.

Given

Total number of protons = 23 protons

We need to find two elements whose atomic numbers sum up to 23.

Atomic number of sodium = 11 (This means that it contains 11 protons)

Atomic number of magnesium = 12

Sum of their atomic number = 11 + 12 = 23

This means that the atoms of which two elements have a combined total of 23 protons are Sodium and magnesium.

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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

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