Polarity is a measure of the uneven distribution of electron density within a molecule. It arises from differences in electronegativity between atoms.

Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond.

Hydrogen cyanide (HCN)

* Polar covalent bond: The carbon-nitrogen bond in HCN is a polar covalent bond because nitrogen is more electronegative than carbon. This creates a partial negative charge on the nitrogen atom and a partial positive charge on the carbon atom.

* Linear geometry: The linear geometry of HCN allows for a net dipole moment, as the bond dipoles do not cancel each other out.

Silicon tetrabromide (SiBr₄)

* Polar covalent bonds: The silicon-bromine bonds in SiBr₄ are also polar covalent bonds, with bromine being more electronegative than silicon.

* Tetrahedral geometry: However, the tetrahedral geometry of SiBr₄ results in the bond dipoles canceling each other out, resulting in a nonpolar molecule.

Conclusion:

Due to its polar covalent bonds and linear geometry, hydrogen cyanide (HCN) has a larger dipole moment and is therefore more polar than silicon tetrabromide (SiBr₄).