Where does “رضائي” come from?

رضائي (Arabic) comes from Persian رضایی, from Persian ـی, from Middle Persian -yk', from Old Persian -𐎡𐎣, from Proto-Indo-Iranian -kas, from Proto-Indo-European -ḱos — -y, -ic.

Ancestry of “رضائي”, step by step

Step	Language	Word	Meaning
1	Persian	رضایی	—
2	Persian	ـی	Forms nouns or adjectives from nouns; Forms...
3	Middle Persian	-yk'	—
4	Old Persian	-𐎡𐎣	of, pertaining to, belonging to, related to
5	Proto-Indo-Iranian	-kas	Creates deadjectival and desubstantival...
6	Proto-Indo-European	-ḱos	-y, -ic

Every word from Proto-Indo-European -ḱos →Every word from Middle Persian -yk' →Every word from Persian ـی →