Arsenic(III) sulphide (yellow) is oxidised completely by conc. HNO3 to arsenic acid H3AsO4 and sulphate. The number of electrons lost per formula unit of As2S3 is

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Arsenic(III) sulphide (yellow) is oxidised completely by conc. $HNO X_{3}$ to arsenic acid $H X_{3} AsO X_{4}$ and sulphate. The number of electrons lost per formula unit of $As X_{2} S X_{3}$ is

Each As goes from +3 to +5:

2 \times 2 = 4

electrons. Each S goes from

- 2

to +6:

3 \times 8 = 24

electrons. Total

4 + 24 = 28

. Counting only As (4) or only S (24) are the usual errors.