Two reactants in a flask at room temperature are producing bubbles of a gas that turn limewater milky. The reactants could be
[amp_mcq option1=”zinc and hydrochloric acid” option2=”magnesium carbonate and hydrochloric acid” option3=”methane and oxygen” option4=”copper and dilute hydrochloric acid” correct=”option2″]
This question was previously asked in
UPSC CDS-2 – 2018
Option A produces hydrogen gas (Zn + 2HCl → ZnCl₂ + H₂), which does not turn limewater milky.
Option C (methane and oxygen) is combustion, which doesn’t occur simply by mixing at room temperature and requires ignition.
Option D (copper and dilute hydrochloric acid) does not react as copper is less reactive than hydrogen.