Question

question 19 of 25
which of the following is the correct name for $\ce{cr_{2}o_{3}}$?

a. chromium trioxide
b. chromium(iii) oxide
c. chromium(ii) oxide
d. dichromium trioxide

Explanation:

To name \( \text{Cr}_2\text{O}_3 \), we first determine the oxidation state of Cr. Oxygen usually has an oxidation state of -2. Let the oxidation state of Cr be \( x \). For the compound to be neutral, \( 2x + 3(-2)=0 \). Solving \( 2x - 6 = 0 \) gives \( 2x=6 \), so \( x = +3 \). In ionic compound naming, for metals with variable oxidation states (like Cr), we use Roman numerals to indicate the oxidation state. So for \( \text{Cr}_2\text{O}_3 \), Cr has a +3 oxidation state, so it's named Chromium(III) oxide. Option A is \( \text{CrO}_3 \) (oxidation state of Cr is +6), option C would be for a compound where Cr is +2 (e.g., \( \text{CrO} \)), and option D is not the standard way to name this compound (we use the oxidation state with Roman numerals for transition metals here).

Answer:

B. Chromium(III) oxide