Question

How boron is a metalloid and carbon is a non-metal ?

(since carbon has 4 electrons in valence shell,therefore it will either donate or gain electrons and so it should be a metalloid)

(since boron has three valence electrons,therefore it will donate and so it should be a metal )

Answer 1

Actually, the metallic character decreases from left to right in a period and non metallic character increases so, boron has half metallic half non metallic character and it is a metalloid.
For tetravalent carbon, the four electrons can not be either lost or gained because it will require much energy and so it shares. But its nature is non metallic.