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JEE Advanced levelSingle correct optionDifficulty 3 of 3bn037

Potassium trioxalatochromate(III) is $K X_{3} [Cr (C X_{2} O X_{4}) X_{3}]$ , where oxalate is $C X_{2} O X_{4} X^{2 -}$ (O is $- 2$ ). What is the SUM of the oxidation numbers of all potassium, chromium and carbon atoms in one formula unit (the three K, one Cr and six C)?

A30
B24
C18
D21

Answer: B

Oxalate:

2 x + 4 (- 2) = - 2

gives C

= + 3

. Complex:

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

gives Cr

= + 3

. Sum

= 3 (+ 1) + 3 + 6 (+ 3) = 24

.

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