Step 1: Valence electron count:
Ti has four electrons outside the argon core: two in $3d$ and two in $4s$. The highest possible oxidation state is therefore $+4$.
Step 2: Stability argument:
At $+4$, the ion has the closed-shell $[Ar]$ configuration with no electron left to lose. This makes $Ti^{4+}$ resist both oxidation and reduction.
Step 3: Rule out the others:
$Ti^{5+}$ is impossible because ionisation would need to remove core electrons, which costs far too much energy. $Ti^{3+}$ and $Ti^{2+}$ can be oxidised further, so they are less stable.
Step 4: Choose:
Option 3 is correct.
Final Answer:
\[ \boxed{Ti^{4+}} \]