is
acidic in nature.
(ii) Chromium is a typical hard metal but mercury is a
liquid.
(iii) The transition metals form a large number of complex
compounds.
(iv) The highest oxidation state of a metal is exhibited
in its oxide or fluoride only.
(v) E° value for the 
couple
is much more positive than that for
or
[5x1]
Or
(i) Complete the following reactions.
(a)
(b)
(ii)Which of the following has the maximum number of
unpaired electrons?
(iii) Give two consequences of lanthanide contraction.
(iv) Based on the data, arrange 
and 
in the
increasing order of stability of + 2 oxidation state.
(v) Calculate spin only magnetic moment of 
[
]
Answer:
(i) With increase in the oxidation state of a given transition
metal, the covalent character of its compound increases and thus acidic
character also increases.
Cr (24) is a hard metal indicating strong interatomic interactions.
This strong interaction is due to valence unpaired electrons in Cr. Greater the
number of unpaired electrons, stronger the interatomic interactions and thus
harder the metal. Hg(80) has very low interatomic interactions due to lack of
unpaired valence electrons and thus is a liquid. [1]
(iii) Transition metals form variety of complexes as
It
is due to
(a) comparatively small size of metal/metal ions
(b) high ionic charge of ions.
(c) availability of vacant d-orbitals for bond formation.
[1]
(iv) Fluorine is the most electronegative element with valency
(-1). It stabilises the highest oxidation state of transition series elements
due to
(a) its highest lattice enthalpy (as in CoF3).
(b) high bond enthalpy due to higher covalent
bonds 
.
(maximum oxidation
state of Mn = + 7) is stable due to multiple bonds between Mn and 0. In each Mn
is tetrahedral surrounded by O-atoms including Mn?O?Mn
[1]
(v) It is due to much larger third ionisation energy of Mn.
This also explains that + 3 state of Mn is rarely shown in compounds.
In case of 
and
stability
of 3d orbitals is low and ionisation is favourable. [1]
Or
(i) 
(thiosulphate)
is oxidised to 
(b) 
is
oxidised to
(ii)
[Ne]
unpaired electron = 0
Thus,
has
maximum number of unpaired electrons. [1]
(a) Zr and Hf, Nb and Ta; and Mo and W have nearly same size.
(b) The elements of 5d-and 4d-transition series resemble
each other than do the elements of 4d-and 5d-series. [1]
(iv) More positive value of reduction potential
indicates more stability of lower oxidation state.
Thus, stability of+ 2 state is
[1]
(v)
N =3 (unpaired electrons)
Magnetic moment 
[1]
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