Concept:Boom sprayers are tractor-mounted implements used for spraying large farm areas.
Explanation:A knapsack sprayer is carried on the back, so it is not tractor-mounted and is meant for smaller fields.
A motorised sprayer is usually a portable power-operated unit, not designed for tractor mounting.
An electrodyne sprayer is a specialised hand-held sprayer, so it is not suitable for large-scale tractor use.
A boom sprayer has a wide boom fitted with several nozzles and is attached to a tractor, making it efficient for covering large farms evenly.
Therefore, the correct tractor-mounted sprayer for large-scale farms is the boom sprayer.
Answer:D. boom sprayer