Mg=220 pm Zn=130 pm the atomic radius difference is larger than 15 They do not satisfy the above condition so it is not complete solubility.
Work Step by Step
For a substitutional solid solution having complete solubility, the following conditions must be satisfied: 1. Atomic radius difference must be less than 15. 2. Both have same electronegativity. 3. Both have same crystal structure. 4.Both have same valence electrons. Mg=220 pm Zn=130 pm the atomic radius difference is much larger than 15