Among the following alkaline earth metal halides, one which is covalent and soluble in organic solvents is :

To determine which alkaline earth metal halide is covalent and soluble in organic solvents, we compare the four options: Magnesium chloride (MgCl₂), Beryllium chloride (BeCl₂), Calcium chloride (CaCl₂), and Strontium chloride (SrCl₂).

1. Electronegativity and ionic radius
The degree of covalent character in a metal‑halide bond depends on the size and charge density of the metal cation. A small, highly charged cation can strongly polarize the electron cloud of the halide anion, leading to covalent character (Fajans’ rules).

2. Be²⁺ versus other alkaline earth cations
Be²⁺ has the smallest ionic radius (≈45 pm) and a high charge density, while Mg²⁺, Ca²⁺, and Sr²⁺ are progressively larger (≈72 pm, 100 pm, 118 pm respectively). The tiny Be²⁺ ion exerts a strong polarizing effect on the chloride ion, pulling electron density toward itself and forming a bond with significant covalent character.

3. Structure of BeCl₂
In the solid state, BeCl₂ adopts a polymeric chain structure where each Be atom is tetrahedrally coordinated to four Cl atoms. This geometry is typical of covalent network compounds rather than purely ionic lattices.

4. Solubility in organic solvents
Because of its covalent nature, BeCl₂ does not form a highly ionic lattice that would be insoluble in non‑polar media. Instead, it can interact with organic solvents (e.g., ether, THF) through coordination to the solvent’s lone pairs, producing soluble complexes such as BeCl₂(THF)₂. This behavior is not observed for the more ionic MgCl₂, CaCl₂, or SrCl₂, which remain largely insoluble in organic solvents.

5. Conclusion
Applying Fajans’ rules and considering the structural and solubility properties, the only alkaline earth metal halide among the list that is covalent and soluble in organic solvents is Beryllium chloride (BeCl₂).