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JEE Advanced levelSingle correct optionDifficulty 3 of 3rx034

Assertion (A): In the tetrathionate ion, $S X_{4} O X_{6} X^{2 -}$ , all four sulfur atoms have oxidation number $+ 2.5$ . Reason (R): The average oxidation number of sulfur in $S X_{4} O X_{6} X^{2 -}$ is $+ 2.5$ . Choose the correct option.

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true

Answer: D

Average:

4 x - 12 = - 2

gives

x = + 2.5

, so R is true. Structure

O X_{3} S - S - S - SO X_{3}

gives the two terminal S

+ 5

and the two inner S

0

, so

(5 + 0 + 0 + 5) /4 = 2.5

but no S has

+ 2.5

. A is false.

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