The correct order of following 3d metal oxides, according to their oxidation numbers is:
(a) CrO$$_3$$ (b) Fe$$_2$$O$$_3$$ (c) MnO$$_2$$ (d) V$$_2$$O$$_5$$ (e) Cu$$_2$$O

We have five neutral oxides of 3d-series metals and we must compare the oxidation numbers of the metal atoms present in them. The basic rule to be used is that, for a neutral compound, the algebraic sum of the oxidation numbers of all the atoms equals zero. In almost every oxide, oxygen has the common oxidation number $$-2$$.

Now we determine the oxidation number of each metal one by one, writing an equation for every compound and solving it.

For $$\text{CrO}_3$$ we let the oxidation number of chromium be $$x$$. We write the equation

$$x + 3(-2) = 0$$

because there is one chromium atom and three oxygen atoms. Simplifying, we have

$$x - 6 = 0$$

so

$$x = +6$$.

For $$\text{V}_2\text{O}_5$$ let the oxidation number of vanadium be $$x$$. There are two vanadium atoms and five oxygen atoms, hence

$$2x + 5(-2) = 0$$

which gives

$$2x - 10 = 0$$

and therefore

$$2x = +10 \quad\Rightarrow\quad x = +5.$$

For $$\text{MnO}_2$$ let manganese have oxidation number $$x$$. With one manganese atom and two oxygen atoms we write

$$x + 2(-2) = 0,$$

so

$$x - 4 = 0$$

and hence

$$x = +4.$$

For $$\text{Fe}_2\text{O}_3$$ let iron possess oxidation number $$x$$. Using two iron atoms and three oxygen atoms:

$$2x + 3(-2) = 0$$

gives

$$2x - 6 = 0,$$

so

$$2x = +6 \quad\Rightarrow\quad x = +3.$$

For $$\text{Cu}_2\text{O}$$ let copper have oxidation number $$x$$. With two copper atoms and one oxygen atom the equation is

$$2x + (-2) = 0,$$

leading to

$$2x - 2 = 0,$$

thus

$$2x = +2 \quad\Rightarrow\quad x = +1.$$

We have now obtained all five oxidation numbers:

$$\text{Cr in CrO}_3 = +6,$$

$$\text{V in V}_2\text{O}_5 = +5,$$

$$\text{Mn in MnO}_2 = +4,$$

$$\text{Fe in Fe}_2\text{O}_3 = +3,$$

$$\text{Cu in Cu}_2\text{O} = +1.$$

To arrange them in decreasing order we simply list the metals in the sequence of their positive oxidation numbers:

$$+6 > +5 > +4 > +3 > +1.$$

Translating back to the actual oxides, the order becomes

$$\text{CrO}_3 \;>\; \text{V}_2\text{O}_5 \;>\; \text{MnO}_2 \;>\; \text{Fe}_2\text{O}_3 \;>\; \text{Cu}_2\text{O}.$$

This order matches exactly with choice (a) > (d) > (c) > (b) > (e), which is listed as Option C in the question.

Hence, the correct answer is Option C.