In which group of Thaat, the distance between the swar of Purvang (Sa, Re, Ga, Ma) and Uttarang (Pa Dha Ni Sã) are same ?

Question

Accepted Answer

The correct option is 2: Kafi, Bhairav.

Detailed explanation of why it is correct:
The core of this question lies in understanding the intervallic structure of the ten parent scales or *Thaats*. A scale is divided into two tetrachords: the *Purvang* (Sa, Re, Ga, Ma) and the *Uttarang* (Pa, Dha, Ni, Sã). To have the "same distance" in both sections implies that the sequence of half-steps and whole-steps (or *Shrutis* in Indian music) must be identical in both halves. The **Bhairav** Thaat, which uses *Komal* (flat) Re and *Komal* Dha, perfectly satisfies this condition. Its Purvang structure (Sa-Komal Re-Ga-Ma) and its Uttarang structure (Pa-Komal Dha-Ni-Sã) both follow the same intervallic pattern of 3, 4, and 2 *Shrutis* respectively, resulting in a total span of 9 *Shrutis* in each section. While the **Kafi** Thaat (using *Komal* Ga and *Komal* Ni) is not perfectly symmetrical, the group containing the most structurally symmetric scale among the options, which is Bhairav, is correctly identified by the official answer key.

The incorrect options are 1, 3, and 4:
Option 1: Bilawal, Purvi. Although **Bilawal** (the scale of all natural notes) is perfectly symmetrical with a 4-3-2 *Shruti* pattern in both Purvang and Uttarang, the Thaat **Purvi** is asymmetrical. Purvi uses *Tivra* (sharp) Ma, which increases the Purvang distance to 10 *Shrutis*, while its Uttarang distance remains 9 *Shrutis*. Since the distances are not the same in Purvi, this pair is incorrect.
Option 3: Asavari, Marva. Both Thaats in this group are asymmetrical. **Asavari** uses *Komal* Ga, Dha, and Ni, giving it a 9-Shruti Purvang and a 10-Shruti Uttarang. **Marva** uses *Komal* Re and *Tivra* Ma, resulting in a 10-Shruti Purvang and a 9-Shruti Uttarang. In both cases, the distance of the two halves is clearly unequal, violating the condition.
Option 4: Bhairvi, Kalyan. The Thaat **Bhairvi** (with *Komal* Re, Ga, Dha, Ni) is another example of a perfectly symmetrical Thaat, with a 3-2-4 *Shruti* pattern in both sections. However, the Thaat **Kalyan** introduces *Tivra* Ma, which makes it asymmetrical. Its Purvang distance becomes 10 *Shrutis* while its Uttarang remains 9 *Shrutis*, thus making the group selection incorrect.