Final answer:
The reaction TiCl4 + 4Na → Ti + 4NaCl is best categorized as a single-replacement reaction, where sodium (Na) replaces chlorine in titanium tetrachloride to produce titanium (Ti) and sodium chloride (NaCl).
Step-by-step explanation:
The reaction TiCl₄ + 4Na → Ti + 4NaCl can be categorized as a single-replacement reaction. In a single-replacement reaction, one element replaces another element in a compound. The reaction provided in the question shows that sodium (Na), which is an element in its solid form, is replacing the chlorine (Cl) in the titanium tetrachloride (TiCl₄). Consequently, elemental titanium (Ti) is formed, along with sodium chloride (NaCl). A characteristic of a single-replacement reaction is its ability to substitute an element for another within a compound such that the product includes a new element and a new compound.
By comparison, a synthesis reaction involves the combination of elements or compounds to form a single new substance, while a double-replacement reaction involves two ionic compounds exchanging their anions or cations. Neither of these definitions fit the given reaction, confirming we are observing a single-replacement reaction.