To answer this question, we need to understand the concept of "ionic compounds" and identify the correct representation for the given compound.

Ionic compounds are compounds that are formed when a metal reacts with a non-metal. They are composed of positive and negative ions held together by strong electrostatic forces called ionic bonds.

In the given options, we are asked to identify the correct representation for an ionic compound. Let's analyze each option one by one:

a) This option represents an ionic compound as it consists of a metal (Mg) and a non-metal (Cl). Magnesium (Mg) is a metal, while chlorine (Cl) is a non-metal. When they react, magnesium loses two electrons to form a positive ion (Mg2+), while chlorine gains one electron to form a negative ion (Cl-). The resulting compound is magnesium chloride (MgCl2).

b) This option does not represent an ionic compound as it consists of two non-metals (O and O). Both oxygen atoms have a high electronegativity and tend to share electrons rather than transfer them. Therefore, this is not an ionic compound.

c) Similar to option b, this option consists of two non-metals (H and Cl). Hydrogen (H) is a non-metal, and chlorine (Cl) is also a non-metal. When non-metals react, they tend to share electrons rather than transfer them. Therefore, this is not an ionic compound.

d) This option represents an ionic compound as it consists of a metal (Na) and a non-metal (F). Sodium (Na) is a metal, while fluorine (F) is a non-metal. Sodium loses one electron to form a positive ion (Na+), while fluorine gains one electron to form a negative ion (F-). The resulting compound is sodium fluoride (NaF).

Based on the analysis, the correct representation for an ionic compound is option A, which corresponds to magnesium chloride (MgCl2).