**Acceleration or Deceleration:**

Acceleration is the rate at which an object changes its velocity. It can be positive or negative, depending on whether the object is speeding up or slowing down. Deceleration is a type of negative acceleration, where the object is slowing down.

In this case, the car is decelerating as it goes from 72 km/h to 36 km/h.

**Calculating Acceleration:**

To calculate the acceleration of the car, we can use the formula:

\[a = \frac{{v_f - v_i}}{{t}}\]

Where:
- a is the acceleration
- \(v_f\) is the final velocity
- \(v_i\) is the initial velocity
- t is the time taken

Given:
- \(v_f = 36\) km/h
- \(v_i = 72\) km/h
- t = 10 sec

**Converting Units:**

Before we can calculate the acceleration, we need to convert the velocities from km/h to m/s. The formula to convert km/h to m/s is:

\[v_{m/s} = \frac{{v_{km/h}}}{{3.6}}\]

Converting the velocities:

\(v_f = \frac{{36}}{{3.6}} = 10\) m/s
\(v_i = \frac{{72}}{{3.6}} = 20\) m/s

**Calculating Acceleration:**

Now, we can substitute the values into the formula:

\[a = \frac{{v_f - v_i}}{{t}} = \frac{{10 - 20}}{{10}} = \frac{{-10}}{{10}} = -1\] m/s²

The negative sign indicates that the acceleration is in the opposite direction to the initial velocity, which is consistent with the car decelerating.

**Conclusion:**

Therefore, the acceleration of the car is -1 m/s². This means that the car is decelerating at a rate of 1 meter per second squared.