Y así se obtiene el cobre, el metal inmortal

Picked one by one from a mixed channel. Transcript check: both title readers certain; 3 of 5 sampled certain picks confirmed by transcript, none failed. Channel rule: Include only the curriculum lesson and worked-example videos whose titles name a subject topic and a school level (ESO/SECUNDARIA, BACHILLERATO/selectividad, UNIVERSIDAD), typically numbered (01, 02...), in math, physics, chemistry or technical drawing; exclude the newer branded, sponsored or magazine-style segments and the test or channel videos.