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JEE Advanced levelSingle correct optionDifficulty 3 of 3bn144

In the thiosulfate ion $S X_{2} O X_{3} X^{2 -}$ the structure is $S - SO X_{3}$ with one S (terminal) bonded only to the other S (central). Electrons of a bond between identical atoms are shared equally. Which choice gives the oxidation numbers (central S, terminal S) and the name of $Na X_{2} S X_{2} O X_{3}$ ?

A $+ 4$ , $0$ ; sodium thiosulfate
B $+ 5$ , $- 1$ ; sodium thiosulfate
C $+ 2$ , $+ 2$ ; sodium thiosulfite
D $+ 5$ , $- 1$ ; sodium sulfite

Answer: B

Sum of S must be

+ 4

(charge

- 2

plus three O at

- 2

). The terminal S has a lone-pair-rich

S X^{-}

-like environment:

- 1

, so the central S is

+ 5

. The name is sodium thiosulfate; sulfite has only one S.

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