Two reactants in a flask at room temperature are producing bubbles of a gas that turn limewater milky. The reactants could be

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Q: 1 (CDS-II/2018)
Two reactants in a flask at room temperature are producing bubbles of a gas that turn limewater milky. The reactants could be

question_subject: 

Science

question_exam: 

CDS-II

stats: 

0,47,22,13,47,8,1

keywords: 

{'limewater milky': [0, 0, 0, 2], 'bubbles': [0, 0, 0, 2], 'magnesium carbonate': [0, 1, 1, 3], 'reactants': [0, 0, 0, 3], 'methane': [0, 0, 0, 5], 'flask': [0, 0, 0, 2], 'gas': [9, 1, 9, 27], 'hydrochloric acid': [1, 0, 3, 0], 'zinc': [1, 0, 0, 2], 'oxygen': [3, 0, 1, 0], 'copper': [1, 0, 1, 1], 'room temperature': [0, 0, 5, 6], 'dilute': [0, 0, 0, 4]}

Option 1: Zinc and hydrochloric acid:

When zinc reacts with hydrochloric acid, it produces hydrogen gas. However, this reaction does not turn limewater milky. Therefore, option 1 is not the correct answer.

Option 2: Magnesium carbonate and hydrochloric acid:

When magnesium carbonate reacts with hydrochloric acid, it produces carbon dioxide gas. This gas can turn limewater milky due to the formation of calcium carbonate, which is insoluble and forms a white precipitate. Therefore, option 2 is the correct answer.

Option 3: Methane and oxygen:

When methane reacts with oxygen, it undergoes combustion to produce carbon dioxide and water. This reaction does not produce a gas that can turn limewater milky. Therefore, option 3 is not the correct answer.

Option 4: Copper and dilute hydrochloric acid:

When copper reacts with hydrochloric acid, it produces copper chloride and hydrogen gas. This reaction does not turn limewater milky. Therefore, option 4 is not the correct answer.

In conclusion, the correct answer is option 2, as the reaction between magnesium carbonate and hydrochloric acid produces carbon dioxide gas, which can turn limewater milky.