The melting points of `AlF_(3)` is `104^(@)` and that of `SiF_(4)` is `-77^(@)` (it sublimes) because:

Options

A. there is a very large difference in the ionic character of the Al-F and Si-F bonds
B. in `AlF_(3), Al^(3+)` interacts very strongly with the neighbouring `F^(-)` ions to given a three dimenstional structure but in `SiF_(4)` no such interaction is possible
C. the silicon ion in the tetrahedral `SiF_(4)` molecules is not shielded effectively from the flouride ions whereas in ` AlF_(3)`, the `Al^(3+)` ion is shielded on all sides
D. the attractive forces between the `SiF_(4)` molecules are strong whereas those between the `AlF_(3)` molecules are weak

Answer

B