The answer to your question is: b
a. Magnesium shares an electron somewhat unevenly from its 3s orbital with the 3p orbital of chlorine producing a mildly polar covalent bond. This option is wrong because Mg does not share electrons it loses electrons.
b. Magnesium loses and electron from the 3s and gives it up to the 3p of chlorine producing an ionic bond. This option is correct, Mg loses one electron and Cl receives it, the bond formed between Mg and Cl is ionic.
c. Magnesium does not react chemically with chlorine because magnesium gives up electrons, but chlorine only shares electrons. This answer is wrong, Mg and Cl react and produce MgCl₂.
d. Magnesium shares an electron from the 3s orbital with the 3p orbital of chlorine producing a covalent bond. Mg does not share electrons and is not able to produce covalent bonds.