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

A)genus

B)family

C)order

D)division

As discussed in

Genus -

A group of related species having more characters in common compared to species of other genera.

- wherein

E.g potato, tomato and brinjal are different species but belong to one genus Solanum.

and,

Family -

A group of closely related genera.

- wherein

E.g Genera Solanum, Petunia and Datura belongs to a family of Solanaceae.

Tomato and potato belong to Genus solanum which belongs to family Solanaceae, where maximum common characteristics can be seen. 

hence option B is correct