I wanna ask if cats are vomiting yellow liquid are they pregnant? Is it normal?

Cats get hairballs from licking their fur. The hairball clogs the digestion so then the cat pukes it up along with whatever food is in the stomach at the moment. It's a part of being a cat. One of these helps a lot: www.amazon.com/Andis-40085-Power-De-Shedder-Small/dp/B001ODZHXC/ref=sr_1_2