Which of the following was NOT a new technology in the 1950s and 1960s?

The option referring to gas masks is the correct choice because gas masks were not a technology introduced in the 1950s or 1960s; rather, they have a much longer history and were widely used during World War I and World War II. The 1950s and 1960s did see developments and improvements in existing technologies such as gas masks, but they were not considered new technologies at that point.

On the other hand, disposable diapers, gas masks, nuclear reactors, and heart pacemakers all represented significant advancements during this period. Disposable diapers became popular in the 1950s due to new materials and manufacturing processes. Nuclear reactors were a major development of the time, particularly in the context of harnessing nuclear energy for power and research. Heart pacemakers were also a medical innovation that emerged in the late 1950s, transforming the treatment of heart conditions. Each of these developments signifies the technological progress of the era, while gas masks were already established long before these innovations.