The ha of 1. druh 2. muh 3.ṣṇuh and 4. ṣṇih is optionally changed to dha before a jhal (all consonant except semi-vowels and nasals) letter or at the end of a word.,
Thus द्रुहः, द्रोढा or द्रोग्धा, मित्रधुक्, मित्रधुट्, मुह, उन्मोग्धा, उन्मोढा, उन्मुक्, उन्मुट्, ष्णुह, उत्स्नोग्धा, उत्स्नोढा, उत्स्नुक्, उत्स्नुट्, ष्णिह, स्नेग्धा, स्नेढा, स्निक्, स्निट् ॥
The root द्रुह would have taken always घ by the last sutra, this makes it optional. The others would not have got घ but for this sutra.
These roots belong to Radhadi sub-class of Divadi gana: and are taught there in this very order (Divadi 89-91). By belonging to Radhadi sub-division, the इट् is optional 7.2.45. Instead of making the sutra वाद्रुहादीनाम्, this longer formation of the aphorism indicates that the rule applies to यङ्लुक् also, as दोध्रुक् or दोध्रुट् ॥ See 7.1.6, for if the roots were taught not specifically but by गण, then the rule would not apply to yan luk.,