* Electronegativity: Boron and Silicon have very similar electronegativity values. Electronegativity is the ability of an atom to attract electrons in a bond. The difference in electronegativity between Boron and Silicon is small, meaning they share electrons almost equally.
* Polarity: A polar bond occurs when there's a significant difference in electronegativity between the atoms, creating a partial positive and partial negative charge on the atoms. In the case of B-Si, the electron sharing is almost equal, so there's no significant charge separation.
In summary: B-Si forms a nonpolar covalent bond because the electronegativity difference between Boron and Silicon is very small.
