The correct option is D 28
The balance reaction given below shows that the number of electrons involved is 28.
+3As22x=6→2AsO3−4+4e−2x−16=−62x=10
S−633x=−6→3SO2−4+24e−3x−24=−63x=18
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As2S3→2AsO3−4+3SO2−4+28e−
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