Is Persian related to Arabic?
No, they are not at all related but they have influenced each other. Persian and Arabic belong to completely different language families, have separate origins. Arabic is a Semitic language — comes from the same family as Hebrew, Aramaic, etc. Persian is an Indo-European language that shares common roots with the languages of Europe and northern India.
Arabic and Persian have a very different grammar and the way the words are constructed is totally different. Persian has a much simpler grammar. Persian has two grammatical cases and one is marked. Arabic has three grammatical cases and all are marked. Persian has no grammatical gender (feminine, masculine, or neuter) — making it easier to learn but Arabic has masculine/feminine nouns!
Persian syntax is subject–object–verb and the Arabic syntax is verb–subject–object. So, theoretically, it’s a lot easier for the Caucasus people (and northern Indian) to learn Persian than it is for native Arabic speakers.
What about the script? The Persian script used in Iran is a modified Arabic script and in Tajikistan Cyrillic script is used. In Arabic there is no P, Ch, Jh, or G (Ga) sounds and “We” (pronounced as whey) is a very common sound which is unknown in Persian. (Even Water becomes Vahter in Iran). The Iranian (much like the northern Indian) have difficulty producing the W sound and consequently the English pronoun “We” always (alvays) comes out as “Vee”!
Yes, there are many Arabic loan words in Persian and Persian language and literature has benefited greatly from Arabic which is the Asian equivalent of Latin. But Persian has as many French loan words too!
“Merci” is the most common way of saying “thank you” in Iran!