Explanation:
Correct option is
D
3
The unbalanced chemical reaction is Al(s)+O
2
(g)→Al
2
O
3
(s)
Balance Al atoms by adding 2 to Al on LHS
2Al(s)+O
2
(g)→Al
2
O
3
(s)
Balance O atoms by adding
2
3
to O
2
on LHS
2Al(s)+
2
3
O
2
(g)→Al
2
O
3
(s)
Multiply the whole equation with 2.
4Al(s)+3O
2
(g)→2Al
2
O
3
(s)
This is the balanced chemical equation. The coefficient of O
2
is 3.