JEE Advanced 2023 — Paper 2 — CHEM-III solution

JEE Advanced2023Paper 2CHEM-III

Consider the following molecules: $B r_{3} O_{8}$ , $F_{2} O$ , $H_{2} S_{4} O_{6}$ , $H_{2} S_{5} O_{6}$ , and $C_{3} O_{2}$ .

Count the number of atoms existing in their zero oxidation state in each molecule. Their sum is____.

Your answer

Solution

Assign oxidation states by inspecting connectivity.

$B r_{3} O_{8}$ : All Br atoms are bonded to oxygens; oxidation states are $+ 6, + 4, + 6$ . No atom has oxidation state zero. Count $= 0$ .

$F_{2} O$ : F is the most electronegative, so O carries $+ 2$ and each F is $- 1$ . No zero oxidation state atom. Count $= 0$ .

$H_{2} S_{4} O_{6}$ (tetrathionate): Structure is $H O_{3} S - S - S - S O_{3} H$ . The two terminal S (bonded to oxygens) are $+ 5$ ; the two middle S atoms are bonded only to other S, giving oxidation state $0$ . Count $= 2$ .

$H_{2} S_{5} O_{6}$ : Similar chain with three middle S atoms bonded only to S, each $0$ . Count $= 3$ .

$C_{3} O_{2}$ (carbon suboxide): $O = C = C = C = O$ . The two terminal C are $+ 2$ ; the central C is bonded only to C, oxidation state $0$ . Count $= 1$ .

Total $= 0 + 0 + 2 + 3 + 1 = 6$ .

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