(B) Venetia
Venetia became a part of unified Italy in 1866, as shown in the map of Italy after unification.
Source: Chapter 1, Section 4 (Unification of Italy)
The map (Fig. 14b) in the textbook clearly labels Venetia – 1866 as the region that joined unified Italy in that year. Sardinia-Piedmont was the base state from which unification began (1858), Sicily joined in 1860, and the Papal State joined last in 1870. For MCQs, always check the map-based data in the chapter.