Answer: SiO 2 (polymeric tetrahedral network via bridging F atoms in solid state).
- A SiO<sub>2</sub> (polymeric tetrahedral network via bridging F atoms in solid state)
- B NaCl, adopting a simple ionic rock-salt lattice under usual circumstances
- C BF<sub>3</sub>, existing as a discrete trigonal planar molecule according to most researchers
- D A simple discrete molecule with little extended network in the majority of cases studied
Correct answer: A. SiO<sub>2</sub> (polymeric tetrahedral network via bridging F atoms in solid state)
Explanation: In the solid state, BeF<sub>2</sub> has a polymeric structure analogous to SiO<sub>2</sub> with bridging fluorides, reflecting Be's tendency to expand its coordination sphere (covalent character).
Each s-block metal ion emits a characteristic flame colour because heating excites electrons to higher energy levels; light is emitted as they fall back, with the colour determined by the specific energy gap.
Concept context
Group 1 (alkali metals) and Group 2 (alkaline earth metals). Learn their reactions with water and air, important compounds like NaOH, Na₂CO₃, and CaCO₃, and anomalous behaviour of lithium and beryllium.