Total distance to be covered:
We need to consider the lengths of both ants since they will pass each other completely. So, the total distance is the sum of their lengths: Distance = Length of ant 1 + Length of ant 2 = 1 cm + 1.2 cm

Convert distance to millimeters:
Since speeds are given in mm/s, we need to convert the distance to millimeters as well.
1 cm = 10 mm (1 centimeter = 10 millimeters)
Therefore, Total distance (mm) = 10 mm (1 cm) + 12 mm (1.2 cm) = 22 mm

Calculate the relative speed:
Since the ants are moving in opposite directions, their speeds add up.
Relative speed = Speed of ant 1 + Speed of ant 2 = 2 mm/s + 3 mm/s = 5 mm/s

Time taken to cover the distance:
Time = Distance / Speed
Time = 22 mm / 5 mm/s = 4.4 seconds

Therefore, it will take the ants 4.4 seconds to completely cross each other.