Two reactants in a flask produce bubbles of gas; it turns lime water into milky. The reactants in the flask are

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Q: 85 (NDA-II/2013)
Two reactants in a flask produce bubbles of gas; it turns lime water into milky. The reactants in the flask are

question_subject: 

Science

question_exam: 

NDA-II

stats: 

0,32,11,7,32,2,2

keywords: 

{'bubbles': [0, 0, 0, 2], 'reactants': [0, 0, 0, 3], 'lime water': [0, 0, 0, 4], 'flask': [0, 0, 0, 2], 'zinc': [1, 0, 0, 2], 'gas': [9, 1, 9, 27], 'magnesium sulphate': [0, 0, 1, 1], 'hydrochloric acid': [1, 0, 3, 0], 'magnesium': [1, 0, 2, 3], 'milky': [0, 0, 0, 2]}

The correct answer is option 2: Magnesium carbonate and hydrochloric acid.

When magnesium carbonate reacts with hydrochloric acid, it produces carbon dioxide gas as one of the products. The bubbling of gas observed in the flask indicates the release of carbon dioxide gas.

Additionally, when carbon dioxide gas is dissolved in water, it forms carbonic acid. Carbonic acid makes the lime water cloudy or milky due to the formation of a precipitate called calcium carbonate. This reaction is commonly used as a test for the presence of carbon dioxide gas.

Option 1, zinc and hydrochloric acid, does produce bubbles of gas, but it does not turn lime water milky. Option 3, magnesium nitrate and hydrochloric acid, and option 4, magnesium sulphate and hydrochloric acid, do not produce bubbles of gas or affect lime water.

Therefore, option 2 is the correct choice as it meets both criteria mentioned in the question.