The angle between a head regulator and entrance of water, for smooth entry of water in a canal is kept as ________?

Which one of the following possesses banana like aroma________?

Those insects which lives in groups, clones or tribes form are called________?

In alluvial river due to the action of centrifugal force, bends are developed by scouring on concave and silting on convex ________?

Diacetyl is present in________?

International day of forest is celebrated on________?