An understanding of ionic crystals is essential to answer the question about their properties. Let us examine each option listed:
Ionic crystals consist of positive and negative ions held together by strong electrostatic forces. These forces require a great deal of energy to break, resulting in high melting and boiling points. Therefore, this statement is correct for ionic crystals.
Ionic crystals, when dissolved in water, dissociate into ions, making the solution capable of conducting electricity. This property classifies them as electrolytes. Hence, this statement is also correct.
Isomorphism refers to two compounds exhibiting the same crystalline form. Many ionic crystals possess this property when different compounds share a similar size and shape. Thus, this statement is true for ionic crystals.
Ionic bonds are non-directional because the electrostatic force of attraction between oppositely charged ions acts equally in all directions. Therefore, directional properties are characteristic of covalent bonds, not ionic bonds. Thus, this statement is incorrect for ionic crystals and is the correct answer to the question.
The correct answer is that ionic crystals do not exhibit directional properties of the bond, as ionic bonds are inherently non-directional.