We are asked to give the name of the fourth oxide fo vanadium.

Get Empirical formula.

100 % = % V + % O

%O = 100% - 56 %

**%O = 44 %**

Recall that ** mass percent** is given by:

$\overline{){\mathbf{\%}}{\mathbf{}}{\mathbf{mass}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{of}\mathbf{}\mathbf{X}}{\mathbf{total}\mathbf{}\mathbf{mass}}{\mathbf{\times}}{\mathbf{100}}}$

Assuming we have **100 g** of the compound, this means we have **56 g C **and **44 g O**.

Now, we need to get the moles of each element in the compound.

The atomic masses are **50.94 g/mol C** and **16 g/mol O**.

**$\mathbf{56}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{V}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{V}}{\mathbf{50}\mathbf{.}\mathbf{94}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{V}}}$ = 1.10 mol V**

**$\mathbf{44}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{O}}{\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}}$ = 2.75 mol O**

Vanadium forms four different oxides in which the percent by mass of vanadium is respectively 76 % , 68 % , 61 % , and 56 % .

Give the name of the fourth oxide.

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