During the formation of MgC{l_2} by Born-Haber cycle, which of the following occurs?A. Ionisation of Mg to M{g^{2 + }}.B. Bond dissociation of C{l_2}.C. Sublimation of Mg.D. Electron gained by Cl.E. All of these.

The formation of MgCl2 by the Born-Haber cycle involves several steps, and each of the options mentioned plays a role in the overall process. Let's break it down:

A. Ionization of Mg to Mg²⁺: This step involves removing one or more electrons from a magnesium atom to form magnesium ions. It is a part of the Born-Haber cycle because it relates to the energy required to ionize magnesium.

B. Bond dissociation of Cl₂: This step involves breaking the bond between the two chlorine atoms in a chlorine molecule (Cl₂). It is also a part of the Born-Haber cycle because it relates to the energy required to dissociate the chlorine molecules.

C. Sublimation of Mg: Sublimation refers to the process of transitioning a substance from a solid directly to a gas without passing through the liquid phase. It is a step in the Born-Haber cycle because it relates to the energy required to convert solid magnesium into gaseous magnesium atoms.

D. Electron gained by Cl: This step involves chlorine atoms gaining electrons to form chloride ions (Cl⁻). It is also a part of the Born-Haber cycle because it relates to the energy released when chlorine gains electrons.

Therefore, the correct answer is:

E. All of these.

All of the mentioned steps (A, B, C, and D) occur during the formation of MgCl2 in the Born-Haber cycle.