Transistors are preferred over mechanical switches for rapid switching operations due to several key advantages:

• Speed: Transistors switch much faster than mechanical switches. They can handle high-frequency operations required in modern electronics. Mechanical switches have a delay caused by the physical movement of components, while transistors can switch in nanoseconds.
• Long Life Span: Transistors are more reliable over time. Mechanical switches wear out due to mechanical movement and friction. In contrast, transistors have no moving parts, reducing wear and enhancing longevity.
• Size and Integration: Transistors are smaller and can be integrated into ICs (Integrated Circuits). This miniaturization facilitates complex circuit designs in compact spaces, essential in contemporary electronic devices.
• Power Efficiency: Transistors consume less power and are more efficient, especially at high speeds, compared to mechanical switches that can cause power loss due to resistance in their contacts.

Therefore, the option "Transistors switch faster and have long life span" is correct. Let's understand why the other options are incorrect:

• "Transistors require manual operation": This is incorrect because transistors are semiconductor devices that are electronically controlled and do not require manual intervention like mechanical switches.
• "Transistors are larger in size": This is false. Transistors are considerably smaller and can be integrated into PCBs, unlike bulky mechanical switches.
• "Transistors consume more power": This is not accurate. Transistors are designed to be power-efficient, significantly more so than mechanical counterparts.

In summary, the superior speed, durability, power efficiency, and miniaturization capabilities make transistors highly suitable for rapid and reliable switching in various electronic circuits.