Learn Farsi: آنها برایش خانه‌ای جدید ساختند، زیرا او یتیم است. - They built a new house for him because he is an orphan.

This word means "for him". It combines the preposition barâ-ye (for) with the pronoun suffix -ash (him/her). Because the base word ends in a vowel, Farsi inserts a "y" sound to smoothly bridge the gap before the vowel of the suffix. This glide gives us barâ-y-ash instead of a clunky double-vowel sound.

Why is the indefinite "a" attached to the noun here (khâne-i jadid) instead of the adjective (khâne-ye jadidi)?

In everyday spoken Farsi, you will usually hear the "a" suffix (-i) attached to the end of the whole phrase: khâne-ye jadidi. However, in written or slightly more formal Farsi, like this sentence, the suffix attaches directly to the noun before the adjective. Because khâne ends in a silent "e", the suffix is written as ای (Alef + Ye) to separate the vowels.

Is zirâ (زیرا) used exactly the same way as chon (چون)?

They both mean "because" and serve the same grammatical purpose, but they belong to different registers. zirâ is a bit more formal and is mostly used in writing or formal speech, whereas chon is what you will hear almost all the time in everyday conversation.

Could we drop the pronoun u (او) in the second half and just say zirâ yatim ast?

Yes, absolutely! Because the verb ast (is) already indicates that the subject is third-person singular, the pronoun (he/she) is grammatically optional. Including it here just adds a little extra clarity or emphasis.