I don't really get why these three columns have the same properties and how do they share the same properties while the number of the outer most electrons vary?

I am thinking the same type oxidation number variance in these transition metals.

For example..

Iron = 3 (2)

cobalt = 2 (3)

nickel = 2 (3)

So, due to valance or electron shielding this block of transition metals has great commonalities here.