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Oxidation number rules and unusual cases
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Difficulty 1 of 3
rx001
What is the oxidation number of chromium in
K
X
2
Cr
X
2
O
X
7
?
A
+
3
B
+
6
C
+
7
D
+
12
Answer: B
Let the oxidation number of Cr be
x
. Then
2
(
+
1
)
+
2
x
+
7
(
−
2
)
=
0
, so
2
x
=
12
and
x
=
+
6
. The value
+
12
results from forgetting that there are two Cr atoms.
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