Amongst LiCl, RbCl, BeCl$$_2$$ and MgCl$$_2$$ the compounds with the greatest and the least ionic character, respectively are:

To determine the compounds with the greatest and least ionic character among LiCl, RbCl, BeCl₂, and MgCl₂, we use the concept of electronegativity difference. Ionic character increases with a greater difference in electronegativity between the atoms. Chlorine (Cl) has an electronegativity of approximately 3.0 on the Pauling scale. The electronegativity values for the other elements are: Lithium (Li) ≈ 1.0, Rubidium (Rb) ≈ 0.8, Beryllium (Be) ≈ 1.5, and Magnesium (Mg) ≈ 1.2.

Calculate the electronegativity difference for each compound:

For LiCl: Electronegativity difference = Electronegativity of Cl - Electronegativity of Li = 3.0 - 1.0 = 2.0.

For RbCl: Electronegativity difference = Electronegativity of Cl - Electronegativity of Rb = 3.0 - 0.8 = 2.2.

For BeCl₂: Since BeCl₂ involves bonds between Be and Cl, the electronegativity difference per bond = Electronegativity of Cl - Electronegativity of Be = 3.0 - 1.5 = 1.5.

For MgCl₂: Similarly, the electronegativity difference per bond = Electronegativity of Cl - Electronegativity of Mg = 3.0 - 1.2 = 1.8.

Now, compare the differences:

• LiCl: 2.0
• RbCl: 2.2
• BeCl₂: 1.5
• MgCl₂: 1.8

The greatest electronegativity difference is 2.2 for RbCl, indicating it has the greatest ionic character. The least electronegativity difference is 1.5 for BeCl₂, indicating it has the least ionic character.

Therefore, the compound with the greatest ionic character is RbCl, and the compound with the least ionic character is BeCl₂.

Now, review the options:

A. MgCl₂ and BeCl₂ → Incorrect, as MgCl₂ is not the greatest.

B. RbCl and MgCl₂ → Incorrect, as MgCl₂ is not the least.

C. LiCl and RbCl → Incorrect, as LiCl is not the greatest and RbCl is not the least.

D. RbCl and BeCl₂ → Correct, as RbCl has the greatest ionic character and BeCl₂ has the least.

Hence, the correct answer is Option D.