Which one of the following options is a viral disease that is usually transmitted by saliva from one person to another?

Mumps is a viral disease that is primarily transmitted through saliva, making it highly contagious among individuals who are in close contact. The mumps virus spreads via respiratory droplets when an infected person coughs or sneezes, but it can also be spread through direct contact with saliva, such as sharing utensils or kissing.

Unlike the other options, mumps specifically has a clear transmission route through saliva, which is why it stands out in this context. This ability to spread through saliva helps explain outbreaks in settings like schools where children are in close proximity.

In contrast, the other diseases listed have different modes of transmission. For instance, acquired immune deficiency syndrome (AIDS) is caused by the human immunodeficiency virus (HIV) and primarily spreads through blood, sexual contact, and from mother to child. Chickenpox, while it can be transmitted through respiratory droplets, is more about airborne transmission rather than direct saliva contact. Hepatitis B, also transmitted through blood and bodily fluids, does not spread via saliva in the same way that mumps does. Thus, mumps is the clear choice for a viral disease typically transmitted by saliva.