An object moving in a straight line is decelerating. which about its acceleration is necessarily true?

Its acceleration is certainly negative.

Explanation:

When an object moving in a straight line decelerates then its velocity certainly decreases.Its acceleration is certainly negative.As we know that acceleration is the rate of change in velocity and the object is decelerating i.e. its velocity is reducing with time.

where:

are final and initial velocities of the object

are final and initial time of observation.

Its SI unit is

It should be d if not then c