Which type of gear train is used in clock mechanism to join hour hand and minute hand?

Answer: Option C

In a clock mechanism, both the hour hand and the minute hand rotate about the same central axis, but they rotate at different angular speeds (the minute hand completes one revolution per hour, while the hour hand completes one revolution in twelve hours).

A reverted gear train is specifically designed so that the input shaft and output shaft are coaxial, which is an essential requirement in clocks where both hands must be mounted on the same axis.

Although a simple gear train can transmit motion between gears, it generally does not satisfy the coaxial shaft requirement when multiple gears are needed to obtain the 12:1 speed reduction within a compact space.

A compound gear train can provide large speed ratios but the input and output shafts are not coaxial, making it unsuitable for clock hands.

An epicyclic gear train is used in applications like automatic transmissions and is unnecessarily complex for clock mechanisms.

Hence, the correct and standard answer in Theory of Machines is Reverted gear train.