A unit cell of an ionic crystal (a) shares some ions with other unit cells; (b) is the same as the formula unit; (c) is any portion of the crystal that has a cubic shape; (d) must contain the same number of cations and anions.

A unit cell in a crystal structure is the smallest component that, reproduced in three dimensions, represents the whole crystal.

(a) A unit cell of an ionic crystal shares some ions with other unit cells: This statement is true. In a unit cell, each corner atom is shared by eight unit cells and each atom on the face center is shared by two unit cells. Therefore, a unit cell shares some of its ions with its neighboring unit cells. (b) A unit cell is the same as the formula unit: This statement is false. A formula unit is the lowest whole number ratio of ions in an ionic compound and does not necessarily represent the actual number of ions in the unit cell of that compound. (c) A unit cell is any portion of the crystal that has a cubic shape: This statement is partly false and true. A unit cell can be in any shape like cubic, tetragonal, orthorhombic, rhombohedral, etc. However, when we refer to a 'unit cell' in general terms, we are often referring to a 'cubic unit cell'. (d) A unit cell must contain the same number of cations and anions: This statement is false. The number of cations and anions in a unit cell depends on the formula of the ionic compound. For example, if the formula of the ionic compound is AB2, the unit cell will contain twice as many B ions (anions) as A ions (cations).

To summarize: (a) is true as unit cells do share ions with each other, (b) is false as unit cells and formula units are different, (c) can be considered generally true specifically for cubic unit cells but false for unit cells of other shapes, and (d) is also false as the number of cations and anions depends on the chemical formula of the ionic compound. So, the correct judgement of the provided statements is True, False, Partially true, and False respectively.