Computers have evolved from the early mainframe computers to the relatively small smart devices with high computing power being used today. Which of the following inventions contributed to reduce the physical size of computers?

Correct option is C

Integrated circuits, also known as chips, are the key invention that contributed to reducing the physical size of computers. They combine millions or even billions of transistors on a single semiconductor chip, which allows for smaller and more efficient circuits.
Therefore, the correct answer is option (c) 
Information Booster: 
 Vacuum tubes are large and fragile, and they consume a lot of power. They were used in early computers, but they were eventually replaced by transistors.
 Transistors are smaller and more efficient than vacuum tubes, but they are still relatively large compared to integrated circuits.
 Cathode ray tubes (CRTs) are used in some displays, but they are not a key component of computers.