Chromium frequently appears in standard exam questions in two main forms: Chromate ($\text{CrO}_4^{2-}$) and Dichromate ($\text{Cr}_2\text{O}_7^{2-}$). In both of these common oxidizing agents, Chromium is always in the $+6$ oxidation state!
Step 1: Understand the question. We must find the oxidation state of chromium in potassium dichromate.
Step 2: Write the formula. Potassium dichromate is $\text{K}_2\text{Cr}_2\text{O}_7$.
Step 3: Note the known states. Potassium is $+1$ and oxygen is $-2$. The whole compound is neutral, so the states must add up to zero.
Step 4: Set up the equation. Let chromium be $x$. \[ 2(+1) + 2(x) + 7(-2) = 0 \] Step 5: Solve for $x$. \[ 2 + 2x - 14 = 0 \implies 2x = 12 \implies x = +6 \] Step 6: Pick the answer. The oxidation state of Cr is $+6$, option (B). \[ \boxed{+6} \]
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