Which of the following does not belong to 3d-series of transition ele…

The answer is 3. Silver. Silver is not a transition element because it does not have a partially filled d-orbital. Transition elements are defined as elements that have a partially filled d-orbital in their ground state or in any of their common oxidation states. Silver has a completely filled d-orbital, so it is not a transition element.

The other three elements, titanium, iron, and vanadium, all have partially filled d-orbitals, so they are all transition elements.

Here is a table of the 3d-series of transition elements:

Element	Symbol	Atomic number	d-orbital configuration
Scandium	Sc	21	3d1
Titanium	Ti	22	3d2
Vanadium	V	23	3d3
Chromium	Cr	24	4s1 3d5
Manganese	Mn	25	3d5
Iron	Fe	26	3d6
Cobalt	Co	27	3d7
Nickel	Ni	28	3d8
Copper	Cu	29	4s1 3d10