3
One from fe
And two from cl2
27 I think beacuse if you subtract
Mg + 1/2 O2 → MgO
1 mol = 24 g of Mg
X mol = 12 g of Mg
x = 0.5 moles of Mg
Mg :MgO = 1:1 (coefficient from equations using mole ratio)
So
0.5 moles of MgO
1 mol MgO = (24+16) g = 40 g
0.5 moles of MgO = 0.5 × 40
= 20 g of MgO produced
The Law of Conservation of Mass states that matter is not created nor destroyed.
Based on this, we can use some addition to find the answer.
3.00 + 1.40 = 4.40 g
Hope this helps :)