(A) Mn shows the highest oxidation state of +7 with oxygen because it can form ppi-dpi multiple bonds using 2p orbital of oxygen and 3d orbital of Mn.
On the hand, Mn shows the highest oxidation state of +4 with fluorine because it can only form a single bond. But the question is why single bond? Majorly it can form a single bond but sometimes it shows partial double bond for example BF3
(B) Let's ask a question. What makes substance so hard or so soft or in between hard-soft? Substances are made from elements which are bonded and hence it is the bond which makes a distinction in hard and soft.Zn has completely filled d-orbital, hence it cannot form metallic bonds while Cr has half-filled d-orbital and can form it. Therefore, Zn is soft, Cr is so hard.
(C) Europium which is a lanthanide has a common oxidation state of +3. And the question why it has so?
The order of penetration of orbitals into the inner core of nucleus is as 4f>5d>6s. Sothe 4f eletrons are the closest to nucleus and attracted by it the most.Now,as successive ionisation increases the net charge on the lanthanide cation,being closest to the nucleus,4f electrons are pulled even more closer than 5d and 6s electrons. Thus is Ln3+,4f electrons are just too strongly pulled by the nucleus to be ionisedfurther as it will require a huge energy for it.So states higher than +3 is generally not seen.
Therefore, Eu2+ must be then good reducing agent as it wants to oxidize itself into Eu3+.
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