Learn Arabic (Modern Standard): إن هذا المشروع لمربح جدا، وهو فرصة استثنائية. - Indeed, this project is truly very profitable, and it is an exceptional opportunity.

This is the Emphatic Prefix (لام التوكيد or لام المزحلقة, the 'slipped' lam) currently being taught. It attaches to the predicate of إنّ to add strong emphasis, translating here to 'truly' or 'surely'. Unlike the preposition لـ (for/to), this emphatic prefix does not affect the noun's case. Since it is the predicate of إنّ, مربح remains in the nominative case with a damma: لَمُربحٌ (la-murbihun).

Since إنّ forces its subject into the accusative case (nasb), why doesn't هذا change its ending?

Demonstrative pronouns like هذا are indeclinable, meaning their endings are fixed and never show case markers. However, it is still grammatically in the accusative position. We can see the effect of إنّ on the following word, المشروع, which acts as a substitute (badal) for هذا. It takes the accusative fatha, being pronounced المشروعَ (al-mashru'a).

How is the word مربح (profitable) derived?

It is the active participle (اسم فاعل) of the Form IV verb أربح (to make a profit), from the root ر-ب-ح (relating to gain or profit). Like all Form IV active participles, it starts with a مُـ (mu-) and has a kasra on the middle root letter, making it مُربِح (murbih).

In the phrase وهو فرصة استثنائية, why is the masculine pronoun هو used when فرصة is feminine?