Is kissing a high-risk behavior, low-risk behavior, or a no-risk behavior for contracting hiv? I'm a high school student and I'm taking a health & physical education course. I'm having a hard time finding the answer to this question.

According . According to the center for disease control (one of the best sources for accurate information): "it depends on the type of kissing. There is no risk from closed-mouth kissing. There is an extremely low-risk from deep, open-mouth kissing if there are sores or bleeding gums and blood is exchanged. Therefore, persons living with HIV should avoid this behavior with a non-infected partner." for the sake of your homework, i'd go with no-risk. Below i've attached the cdc website on HIV transmission. Maybe you'll get extra credit for specifying the no-risk vs. Low risk behaviors.
Low risk. The HIV virus is really quite fragile and is generally only transmitted through blood to blood contact.