Wxplain the following giving suitable reson.
(a). Transitin metals of 3d-series doe not react readily with dilute acids to liberate hydrogen although they have high negative reduction potential values. Explain.
(b). The atomic radii of the elements in a transition series do not vary much while they do vary in the case of s and p-block elements. Explain.
(c). The second and third members in each group of the transition elements group of the transition elements have similar atomic radii. Explain.

Explanation

(a). Solution: Most of the transition metal have the tendency to form a protective layer of their oxides on the surface. This oxide layer is somewhat inert and does not permit the metals to react with dilute acids to liberate hydrogen.
(b). There are two operating effect namely7 nuclear charge effect and screeening effect which oppose each other. Due to increase in nuclear charge from member to member in a tranition series, the atomic radii ten to decrease. At the same time, the addition of extra electrons one by one to `(n-1)` d-orbitals provides the screening effect. As the number of d electrons increases, the screening effect increases and this tends to increase size. Due to these opposing tendencies, There is a very small change in the atomic radii in a transition series. IN s and p-block elements the extra electron is addedto same s or p-block elements, the extra electron is added to same s or p-subshell which does not exert screening effect and hence, the atomic radii decreases considerably in a period due to increase in nuclear charge.
(c). This is due to lanthanide contraction by the member of 4f-series which occupy a position between lanthanum `(Z=57`, a first memeber of third transition series) and hafnium `(Z=72`, second member of 3rd transition series).
2nd transition series 3rd transition series The pairs of elements such as `Zr-Hf,Hb-Ta,Mo-W`, Ets. Possess nearly the same atomic radii and almost the same properties.