ANSWER
The correct answer is A
EXPLANATION
From the equation [tex]Fe + O_2 \rightarrow Fe_2O_3[/tex]
L.H.S. Â Â Â Â Â Â Â Â
Fe = 1 Â Â Â Â Â Â Â Â Â Â Â Â
O Â =2 Â Â Â
        Â
R.H.S
Fe =2
O Â =3
Now, let try to balance the oxygen atoms first,
To do this, we know the Least Common Multiples of 2 and 3 is 6
To get 6 atoms of oxygen at L.H.S Â multiply 2 by 3 and on the R.H.S, multiply 3 by 2
L.H.S. Â Â Â Â Â Â Â Â Â Â Â Â
[tex]O=2\times3=6[/tex] Â Â Â
R.H.S
[tex]O=3\times2=6[/tex] Â
This means that, 3 should be in front of [tex]O_2[/tex] at the L.H.S and 2 should come before [tex]Fe_2O_3[/tex] in the R.H.S of the equation
Now, we have
L.H.S. Â Â Â Â Â Â Â Â Â Â Â Â
Fe = 1 Â Â Â Â Â Â Â Â Â Â Â Â Â
O Â = Â 6 Â Â Â Â Â Â Â Â Â Â Â Â
R.H.S
Fe =4
O Â =6
The equation is still not balanced since Fe is not balance
Â
The Least Common Multiple of  1 and 4 is 4
Which means that we need to multiply 1 by 4 at the L.H.S and 4 by 1 at the R.H.S
L.H.S. Â Â Â Â Â Â Â Â Â Â Â Â
[tex]Fe=1\times4=4[/tex] Â Â Â
R.H.S
[tex]Fe=4\times1=4[/tex] Â
We now, have
L.H.S. Â Â Â Â Â Â Â Â Â Â Â
Fe= 4 Â Â Â Â Â Â Â Â Â Â Â Â Â
O=6 Â Â Â Â Â Â Â Â Â Â Â Â
R.H.S
Fe =4
O=6
Hence the balanced equation is
[tex]4Fe +3O_2\rightarrow 2Fe_2O_3[/tex]
