Which virus is a member of the herpes group and is known to cause infectious mononucleosis?

The Epstein Barr Virus (EBV) is the virus that is a member of the herpes group and is specifically known for causing infectious mononucleosis, often referred to simply as "mono." This virus is highly prevalent and is transmitted primarily through saliva, which is why it's sometimes called the "kissing disease." Symptoms of infectious mononucleosis often include fever, sore throat, swollen lymph nodes, and fatigue.

To understand why this answer stands out, consider the other viruses listed: while varicella-zoster virus is responsible for chickenpox and herpes simplex virus leads to cold sores and genital herpes, neither of these is associated with infectious mononucleosis. Cytomegalovirus, although also a member of the herpes family, can cause similar symptoms but is not the primary cause of mono like EBV is. Therefore, when identifying the virus known for causing infectious mononucleosis, Epstein Barr Virus is clearly the correct choice.