Answer:
6
Explanation:
You have the unbalanced chemical reaction:
BF3 + Li2SO3 ⇒ B2(SO3)3 + LiF
Knowing that there are 2 atoms of boron in the products, we need to adjust that element putting 2 as coefficient of BF3.
2BF3 + Li2SO3 ⇒ B2(SO3)3 + LiF
Then, we need to balance fluor. There are 6 atoms of F in the reactants, for that reason, we write 6 in the lithium fluoride.
2BF3 + Li2SO3 ⇒ B2(SO3)3 + 6LiF
Finally, sulfur and oxygen have to be adjusted. 3 before lithium sulfite is enough to balance the chemical reaction.
2BF3 + 3Li2SO3 ⇒ B2(SO3)3 + 6LiF