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Actinoid contraction is greater from element to element than lanthanoid contraction. The reason behind it is the poor shielding effect of  5 (in actinoids) orbitals than 4 orbitals( in lanthanoids). As a result, the effective nuclear charge experienced by valence electrons is more in actinoids than lanthanoids elements.
ion is unstable in aq. solution and disproportionate to give  and  The hydration energy release during the formation of compensates the energy required to remove an electron from -configuration.
Atomic number (Z)= 27 So the electronic configuration cobalt () is  ion means, it loses its two electrons and become  configuration. And it has 3 unpaired electrons So,  , where n = no. of unpaired electron by putting the value of n= 3 we get,                   
Reducing agents are those which lose the electrons easily. Here or ,the reduction potential value of  is more than that of .Hence  easily gets oxidised to  (attains configuration). Hence  is better reducing agents.
Oxygen and fluorine are strong oxidising agents and both of their oxides and fluorides are highly electronegative in nature and also small in size. Because of these properties, they can oxidise the metal to its highest oxidation states.
The irregular variation in ionisation enthalpies is due to the extra stability of the configuration like  because these states are extremely stable and have high ionisation enthalpies. In the case of chromium () has low 1st IE because after losing one electron it attains stable configuration (). But in the case of Zinc (), the first IE is very high, because we remove an electron from a stable...
    The value for metal depends on- Sublimation energy Ionisation energy Hydration energy Copper has a high value of atomisation enthalpy and low hydration energy. Thus, as a result, the overall effect is   for copper is positive.
In 3d series of transition metals Manganese shows largest number of oxidation states because it has highest number of unpaired electrons in its -orbitals.So, that by removing its all electrons we get different oxidation states. Example-  etc.

The enthalpy of atomisation of zinc is lowest due to the absence of unpaired electron,which ie responsible formetallic bonding in the elements.Therefore, the inter-atomic bonding is weak in zinc(Zn). Hence it has low enthalpy of atomisation.

Silver atom(atomic no. = 47) has completely filled d-orbital in its ground state(4). However, in +2 oxidation state, the electron of d-orbitals get removed. As a result, the d-orbital become incomplete() . Hence it is a transition element.