Wavelength is defined as the distance between two consecutive nodes or two consecutive antinodes in a wave. In this question, we are given a string of length 12 cm and it is mentioned that there is formation of nodes.

Let's analyze the formation of nodes in the string:

1. Node at each end: The question states that there is a formation of nodes at all five nodes, including terminal nodes. Since there are two terminal nodes (at each end of the string), they are also nodes.

2. Remaining three nodes: As there are five nodes in total and two of them are terminal nodes, the remaining three nodes must be formed within the string itself.

Now, let's calculate the distance between the nodes:

- Distance between the two terminal nodes: Since the string has a total length of 12 cm, the distance between the two terminal nodes is 12 cm.

- Distance between the remaining three nodes: As there are three nodes formed within the string, the distance between them can be calculated by subtracting the distance between the terminal nodes from the total length of the string.

Therefore, the distance between the remaining three nodes is (12 cm - 12 cm) = 0 cm.

Since the distance between two consecutive nodes is 0 cm, it means that the nodes are overlapping each other. This indicates that the nodes are formed at the same point in the string, resulting in the formation of a standing wave.

Since the wavelength is defined as the distance between two consecutive nodes, and in this case, the distance is 0 cm, we can conclude that the wavelength of the waves formed is 0 cm.

However, in the given options, the closest value to 0 cm is 6.0 cm. Therefore, the correct answer is option A) 6.0 cm.