Given information:
Acceleration (a) = 10 m/s^2
Time (t) = 20 seconds

Calculating the distance travelled:
To calculate the distance travelled, we need to find the velocity (v) of the particle at the end of the 12th second, which can be done using the equation:

v = u + at

Where:
v = final velocity
u = initial velocity
a = acceleration
t = time

To find the initial velocity, we can use the formula:

u = v - at

Now, let's calculate the initial velocity:

u = v - at
u = 0 - (10 * 12)
u = -120 m/s

Calculating the velocity at the end of the 12th second:
Using the equation:

v = u + at

v = -120 + (10 * 12)
v = -120 + 120
v = 0 m/s

Calculating the distance travelled:
To find the distance travelled, we can use the equation:

s = ut + (1/2)at^2

Where:
s = distance
u = initial velocity
t = time
a = acceleration

Substituting the values:

s = (-120 * 12) + (1/2)(10)(12^2)
s = -1440 + (1/2)(10)(144)
s = -1440 + (1/2)(10)(144)
s = -1440 + 720
s = -720 m

Explanation:
The particle initially had an acceleration of 10 m/s^2. To find the distance travelled in the 12th second, we first calculate the initial velocity using the formula v = u + at. Then, we find the velocity at the end of the 12th second by substituting the values into the same equation.

After finding the velocity, we can use the equation s = ut + (1/2)at^2 to calculate the distance travelled. By substituting the values into the equation, we find that the particle has travelled a distance of -720 m. The negative sign indicates the direction of motion, which means the particle has moved in the opposite direction to its initial position.

Therefore, the particle has travelled a distance of 720 meters in the 12th second.