Explanation:

- Option 1: Transistors

- Correct Answer

- Transistors replaced vacuum tubes in electronic devices. They're smaller, more reliable, and energy-efficient.

- Option 2: Microchips

- Microchips contain multiple transistors and other components. They came after transistors were established.

- Option 3: Resistor networks

- These are used for specific circuit applications, not as a replacement for vacuum tubes.

- Option 4: Electromagnetic coils

- These are components used in various applications but didn't replace vacuum tubes.

- Option 5: Diodes

- Diodes provide one-way current flow. They did not replace vacuum tubes entirely.