Answer
This is a combination reaction.
Work Step by Step
In a combination reaction, two compounds/elements are combined to form a single product.
And the pattern for that type of reaction is: "A + B $--\gt$ AB"
For: $4Al(s) + 3O_2(g) --\gt 2Al_2O_3(s)$, A is $Al$, and B is $O_2$.
