The average velocity for a trip has a positive value. isit
possible for the instantaneous velocity at any point during thetrip
to have a negative value? justify the answer.

Yes, it's possible.

Explanation:

The average velocity is a mean value:

.

during that displacement, it may occur that the acceleration would negative at any time so at that moment if the velocity goes in the same direction with the acceleration, the velocity will be negative, it may take just a few moments and then go positive again. The velocity can also take negative values if for a moment the object was going backward (opposite direction). so the average velocity only means that the major of the velocity was positive.

see earlier