Answer
The compound isolated by Berzelius is selenium. It's a nonmetallic element that belongs to Group 16 (chalcogens) and Period 4 of the periodic table. It is a brittle, lustrous, grayish-red metalloid. It is an analog of sulfur and tellurium. Selenium has various allotropes with the stable hexagonal "metallic" selenium and red "amorphous" selenium being the most common.