Which of the following bacterial diseases is contagious person to person?

Pneumonic plague is contagious from person to person because it is an infectious disease that specifically affects the lungs and can be transmitted through respiratory droplets. This means that when an infected person coughs or sneezes, they can release the bacteria into the air, which can then be inhaled by someone nearby, leading to infection.

In contrast, other options like tularemia, brucellosis, and plague do not typically spread directly between humans. Tularemia is primarily spread through contact with infected animals or their tissues, and brucellosis is generally transmitted through consuming contaminated animal products or being in contact with infected animals. Similarly, while plague can transmit via fleas or through direct contact with infected materials, the bubonic form of the disease is not transmitted between humans via respiratory means, unlike the pneumonic form. Thus, pneumonic plague stands out as the only one in this set that is person-to-person contagious.