Which is not an example of convergent evolution?

The correct answer is Option (3) → Thorns of Bougainvillea and tendrils of Cucurbita

Convergent evolution gives analogous structures: different structures doing the same job.

Option (1) Eye of an octopus and eye of man — An example of convergent evolution. NCERT gives the eye of the octopus and of mammals as an example of analogy. The eyes are built differently but both form images, so they come from convergent evolution.

Option (2) Sweet potato and Potato — An example of convergent evolution. NCERT says sweet potato (a root modification) and potato (a stem modification) are another example of analogy: different organs doing the same job of storing food.

Option (3) Thorns of Bougainvillea and tendrils of Cucurbita — Not an example of convergent evolution. Both are modified stems doing different jobs: homologous organs, from divergent evolution.

Option (4) Wings of butterfly and wings of an Eagle — An example of convergent evolution. Wings of butterfly and of birds look alike and both are used for flight, but they are not anatomically similar. They are analogous structures, the result of convergent evolution.

NCERT Extract:
What Are the Evidences for Evolution? – “… Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions. Hence, analogous structures are a result of convergent evolution - different structures evolving for the same function and hence having similarity. Other examples of analogy are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins.”
What Are the Evidences for Evolution? – “… In plants also, the thorn and tendrils of Bougainvillea and Cucurbita represent homology (Figure 6.3a).”
What Are the Evidences for Evolution? – “… Sweet potato (root modification) and potato (stem modification) is another example for analogy.”