What type of spraying used in plant protection operation in which total volume of liquid applied amounts to a few ml per acre and is mainly used in aircraft spraying?

Correct option is C

ULV spraying (Ultra-Low Volume spraying) uses minimal liquid (a few ml per acre) and is commonly employed in aerial applications for pest and disease control in large areas.
Explanation of other options:
(a) Foam Spraying: Used for localized spraying and does not involve low volume.
(b) Low Volume Spray: Requires more liquid than ULV spraying.
(d) High Volume Spray: Involves significant liquid amounts, unsuitable for aerial applications.