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When a flask containing sodium thiosulfate is placed over a paper marked with ‘X’ and HCl added to it, the ‘X’ seems to disappear when looked through the flask. Why?

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in Chemistry – Class 12 by (188k points)
When a flask containing sodium thiosulfate is placed over a paper marked with ‘X’ and HCl added to it, the ‘X’ seems to disappear when looked through the flask. Why?

(a) Because of formation of sodium chloride

(b) Because of sulfur precipitating

(c) Because of release of yellowish chlorine gas

(d) Because of dissolution of sulfur

The question was posed to me in final exam.

Question is from P-Block Elements topic in portion P-Block Elements of Chemistry – Class 12

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Correct choice is (b) Because of sulfur precipitating

The explanation is: When sodium thiosulfate is treated with hydrochloric acid, sodium chloride is formed along with elemental sulfur. This yellow sulfur precipitates and causes the mark ‘X’ to fade away.

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