1.

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

Answer»

there is a very large difference in the ionic character of the AL-F and Si-F bonds
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
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
the ATTRACTIVE FORCES between the `SiF_(4)` molecules are strong whereas those between the `AlF_(3)` molecules are weak

Answer :B


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