The gear train usually employed in clocks is

Explanation:

Reverted gear train:

When the axes of the first gear and the last gear are co-axial, then the gear train is known as a reverted gear train. The reverted gear trains are used in automotive transmissions, lathe back gears, industrial speed reducers, and in clocks (where the minute and hour hand shafts are co-axial).

Advantages:

• The epicyclic gear trains are useful for transmitting high-velocity ratios with gears of moderate size in a comparatively lesser space.
• The epicyclic gear trains are used in the back gear of lathe, differential gears of the automobiles, hoists, pulley blocks, wrist-watches, etc.