Answer is: selenium (Se).
Black selenium (allotrope modification) is irregular, complex, brittle and lustrous solid.
The commercial use for selenium is glassmaking.
Selenium is an element (nonmetal) with atomic number 34 (34 protons and 34 electrons)-
Electronic configuration of selenium atom: ₃₄Se 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁴.
Answer: Option (a) is the correct answer.
Explanation:
Metals are malleable and ductile whereas non-metals are brittle in nature.
Out of the given options cobalt, platinum and zinc are all metals except selenium which is a non-metal.
Being a non-metal, selenium is brittle in nature.
Thus, we can conclude that selenium is likely to be the most brittle out of the given options.
