ㄴ 거 주다

give me the [adjective] one

-ㄴ 거 turns a describing word into 'the ~ one' and 주다 asks for it or hands it over: 따뜻한 거 주세요 'a hot one, please', 큰 거 줄까 작은 거 줄까? 'want the big one or the small one?'. This is the ordinary way to pick out an item by a quality instead of naming it, at a counter or between friends. 거 is the spoken contraction of 것.

Register: everyday spoken