It is not possible to construct a triangle when the lengths of its sides are

1. 6 cm, 7 cm, 8 cm

2. 4 cm, 6 cm, 6 cm

3. 5.3 cm, 2.2 cm, 3.1 cm

4. 9.3 cm, 5.2 cm, 7.4 cm

We know that in a triangle, the sum of any two sides of a triangle is greater than the third side.

But, when sides are 5.3 cm, 2.2 cm, 3.1 cm.

2.2 + 3.1 = 5.3 cm.

Here, sum of two sides is equal to third side.

Hence, construction of triangle with sides 5.3 cm, 2.2 cm, 3.1 cm is not possible.

Hence, Option 3 is the correct option.