How is the variability in oxidation states of transition metals different forming that of non-transition metals?  illustrate with an example.
                The number of variable oxidation states in transition metals is due to the participation of (n-1) d electrons in addition to ns electrons in the bond formation. Thus, they exhibit a large number of variable oxidation states. But non-transition metals generally of s-block do not show variable oxidation states because, by the loss of s-electrons, they acquire stable configuration.
Why do transition elements form colored compounds?
                Most of the d-block elements form colored compounds because of the presence of unpaired electrons in these. The electrons absorb radiations of one colour from white light for excitation from one energy level to another within the same d-subshell. Thus, the transmitted light appears coloured. If the compound absorbs blue light, then it appears orange and vice versa. Zn, Cd, and Hg are white because of the absence of unpaired electrons in the d-orbital’s.
Why Zn, Cd, and Hg are not regarded as transition elements?
                These metals do not have any partially filled orbital but are still regarded as transition elements. The reason is that these are quite similar to other transition elements in their chemical properties.
Why do transition elements show similarities along the horizontal period as well as down a vertical colour?
                The properties of an element mainly depend upon its valence shell configuration. In a period of d-block, the electrons are filled in the inner (n-1) d sub-shell while the valence shell remains unaffected. As a result, transition elements show similar behavior along the horizontal period. These elements also showed similar behavior down a vertical column due to the same valence shell configuration.
Most of the d-block elements are paramagnetic but zinc, cadmium, and mercury are diamagnetic. Why?
                Most of the d-block elements and their compounds are paramagnetic i.e. they are attracted by the magnetic field. It is because of the unpaired electrons in them. The spin movement of those unpaired electrons generates a magnetic field which can interact with the applied field. Zn, Cd, and Hg are diamagnetic due to the absence of unpaired electrons in them.
Explain why d-block elements are hard metals but Zn, Cd, and hg are soft.
                All the d-block elements are metals due to their low ionization potentials and the presence of vacant orbitals. These elements are harder and non-brittle than s-block elements. The reason is that these can form covalent bonds by the overlap of their partially filled d-orbitals. Zn Cd and hg are soft due to the absence of partially filled orbitals in them.

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