Comprehension:
TRANSITION METALS
All the transition elements display typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre. With the exceptions of Zn, Cd, Hg and Mn, they have one or more typical metallic structures at normal temperatures.
The transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility. Their melting and boiling points are high. The high melting points of these metals are attributed to the involvement of greater number of electrons from (n–1)d in addition to the ns electrons in the interatomic metallic bonding. In any row the melting points of these metals rise to a maximum at d5 except for anomalous values of Mn and Tc and fall regularly as the atomic number increases.
The maxima at about the middle of each series indicate that one unpaired electron per d orbital is particularly favourable for strong interatomic interaction. In general, greater the number of valence electrons, stronger is the resultant bonding. Since the enthalpy of atomisation is an important factor in determining the standard electrode potential of a metal, metals with very high enthalpy of atomisation (i.e., very high boiling point) tend to be noble in their reactions.
Which of the 3d series transition metal exhibits maximum number of oxidation states?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Manganese
Transition metals show variable oxidation states because the energies of the (n−1)d and ns orbitals are very close, so electrons from both can be lost or shared. In the 3d series, the number of oxidation states rises towards the middle, as more electrons become available, and then falls as the d electrons pair up:
Sc: +3
Ti: +2, +3, +4
V: +2, +3, +4, +5
Cr: +2, +3, +4, +5, +6
Mn: +2, +3, +4, +5, +6, +7
Fe: +2, +3, +4, +6; Co: +2, +3, +4; Ni: +2, +3, +4
Cu: +1, +2; Zn: +2
Manganese (Z = 25, [Ar]3d54s2) can use all seven of its 4s and 3d electrons, so it shows every oxidation state from +2 to +7. So the 3d metal with the maximum number of oxidation states is manganese.
Why the other options are incorrect
Option (1) Scandium — Incorrect. Sc (Z = 21, [Ar]3d14s2) shows essentially only the +3 state, reached by losing all three outer electrons.
Option (2) Copper — Incorrect. Cu (Z = 29, [Ar]3d104s1) shows only +1 and +2.
Option (4) Vanadium — Incorrect. V (Z = 23, [Ar]3d34s2) has only five 4s and 3d electrons, so it shows four oxidation states, +2 to +5, fewer than manganese.
NCERT (2026-27 edition):
Oxidation States – “… The elements which give the greatest number of oxidation states occur in or near the middle of the series. Manganese, for example, exhibits all the oxidation states from +2 to +7. The lesser number of oxidation states at the extreme ends stems from either too few electrons to lose or share (Sc, Ti) or too many d electrons (hence fewer orbitals available in which to share electrons with others) for higher valence (Cu, Zn).”