Explanation:

- Option 1: Notochord is present

- Chordates possess a notochord at some stage in their lifecycle.

- This flexible rod provides structural support.

- Correct Answer

- Option 2: Heart is dorsal or laterally placed or absent

- This statement is incorrect.

- Chordates typically have a ventrally placed heart, not dorsal or lateral.

- Option 3: A post-anal tail is absent

- This is incorrect for chordates.

- A post-anal tail is a defining feature of chordates.

- Option 4: Double ventral solid nerve cord

- This is inaccurate for chordates.

- They have a single, hollow dorsal nerve cord.