The element that can be refined by distillation is:

To determine which element can be refined by distillation, we examine the physical properties of the given metals, particularly their boiling points.

Distillation is a refining technique used for metals with relatively low boiling points. In this process, the impure metal is heated until it vaporizes. The vapours are then condensed to obtain the pure metal, while the non-volatile impurities remain behind.

Let us analyze each of the given elements.

(A) Nickel (Ni)

Nickel has a high boiling point and is not refined by distillation. It is commonly purified by the Mond process, a vapour phase refining technique in which nickel reacts with carbon monoxide to form volatile nickel tetracarbonyl, which is subsequently decomposed to obtain pure nickel.

(B) Zinc (Zn)

Zinc possesses a comparatively low boiling point (approximately $$907^\circ\text{C}$$). Along with other Group 12 elements, it has a completely filled $$d^{10}$$ configuration, resulting in relatively weak metallic bonding. Consequently, zinc vaporizes readily and can be efficiently purified by distillation.

(C) Tin (Sn)

Tin is generally refined by liquation because of its low melting point. In this process, the impure metal is heated on a sloping hearth so that the molten metal flows away from the solid impurities.

(D) Gallium (Ga)

Gallium is typically purified by zone refining, especially for semiconductor applications where extremely high purity is required. This method relies on the greater solubility of impurities in the molten state than in the solid state.

Hence, among the given options, zinc is the metal that can be refined by distillation due to its relatively low boiling point.

Therefore, the correct answer is

$$
\boxed{\text{(B) Zinc}}.
$$