Answer
(a) 2SO$_2$ + O$_2$ $-->$ 2SO$_3$
(b) sulfur trioxide
Work Step by Step
(a) We see the following equation represented by the diagram:
4SO$_2$ + 2O$_2$ $-->$ 4SO$_3$
We want to use the lowest whole number coefficients possible. We see that we can divide each coefficient by 2 to get the lowest whole number coefficients possible to get:
2SO$_2$ + O$_2$ $-->$ 2SO$_3$
(b) Since this is a molecular compound, we add prefixes to denote the number of cations and anions in the compound. Because there is only one atom of sulfur in the compound, we don't give add a prefix to it. With oxygen, there are three atoms of oxygen in the compound, so we add the prefix $tri-$ to its name and then change the ending of the element to $-ide$. The name of the product compound is sulfur trioxide.
