You may be confusing Islamic for Arabic. They're not the same, even though they overlap. If you call someone Arabic, you're describing their ethnic group; if you call someone Muslim, you're describing their religion. Not all Arabs are Muslims, and not all Muslims are Arabs.
Persians are the largest ethnic group in Iran. Their language is Indo-European. (Arabic is Semitic.) Actually, Wikipedia says only about 3% of Iranians are Arab, which is a lot lower than I thought it was... hmm.
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You may be confusing Islamic for Arabic. They're not the same, even though they overlap. If you call someone Arabic, you're describing their ethnic group; if you call someone Muslim, you're describing their religion. Not all Arabs are Muslims, and not all Muslims are Arabs.
Persians are the largest ethnic group in Iran. Their language is Indo-European. (Arabic is Semitic.) Actually, Wikipedia says only about 3% of Iranians are Arab, which is a lot lower than I thought it was... hmm.