The common characteristics between tomato and potato will be maximum at the level of their

The correct option is family.

To understand why, let us look at the taxonomic hierarchy of classification, which is organized from the highest (most general) to the lowest (most specific) level:
Kingdom ⇒ Division ⇒ Class ⇒ Order ⇒ Family ⇒ Genus ⇒ Species

In this classification hierarchy, as we move down from Kingdom to Species, the number of common characteristics shared by the organisms increases. Therefore, the lower the taxonomic category two organisms share, the higher the number of common characteristics they will have in common.

Let us look at the taxonomic classification of potato and tomato:
1. Potato belongs to the genus Solanum (scientific name: Solanum tuberosum).
2. Tomato has traditionally been classified under the genus Lycopersicon (scientific name: Lycopersicon esculentum).
Since they belong to different genera, they do not share the genus level. The lowest taxonomic category that both tomato and potato share is their family, which is Solanaceae (commonly known as the nightshade family).

Among the given choices (family, genus, division, order), the lowest taxonomic level they share is their family, meaning their common characteristics will be maximum at the level of their family.