How many different alkyl chlorides result from C4H10 and chlorine?

Let's say there's a reaction $\ce{C4H10 + Cl2}$ taking place under UV light. How many different alkyl chlorides do we obtain?


I'm not sure if the resulting molecule would be monochlorinated or dichlorinated? My guess was monochlorinated, as $\ce{HCl}$ is also going to be a product. And I assumed there would be 2 different alkyl chlorides as there are two different possibilities for a chlorine to be attached to a carbon of a butane. But I guess I was wrong as the answer the book gives is 4 and not 2. How can the book’s answer be rationalised?


