One of the following is not a principal Upanishada.Kaṭha Upanṣadb.Māṇḍūkya Upaniṣadc.Chāndogya Upaniṣadd.Akṣi Upaniṣad

The question states that one of the options is not a principal Upanishad. The options given are:

a. Kaṭha Upaniṣad b. Māṇḍūkya Upaniṣad c. Chāndogya Upaniṣad d. Akṣi Upaniṣad

To determine which one is not a principal Upanishad, we need to identify the principal Upanishads and compare them with the given options.

The principal Upanishads are a collection of ancient Indian texts that are considered the most important and authoritative Upanishads. There are traditionally considered to be ten principal Upanishads, which are:

1. Isha Upanishad
2. Kena Upanishad
3. Katha Upanishad
4. Prashna Upanishad
5. Mundaka Upanishad
6. Mandukya Upanishad
7. Taittiriya Upanishad
8. Aitareya Upanishad
9. Chandogya Upanishad
10. Brihadaranyaka Upanishad

Comparing the given options with the list of principal Upanishads, we can see that:

a. Kaṭha Upaniṣad is one of the principal Upanishads. b. Māṇḍūkya Upaniṣad is one of the principal Upanishads. c. Chāndogya Upaniṣad is one of the principal Upanishads. d. Akṣi Upaniṣad is not listed as one of the principal Upanishads.

Therefore, the correct answer is d. Akṣi Upaniṣad is not a principal Upanishad.