Solution x mixed with magnesium chloride solution to form a white precipitate. the white precipitate obtained and reacted with dil hcl to give colourless gas bubbles turn lime water milky
what is solution x?

Solution X might be a solution of carbonate ions .

The question doesn't tell much about the positive ion in solution X. The ion itself shall not react with carbonate ions to form a precipitate. For that, cations from group 1 metals will work. For example, X can be a solution of sodium carbonate, which contain a large number of sodium ions .

Explanation:

Start with the first observation:

"Solution X mixed with magnesium chloride solution to form a white precipitate."

A solution of magnesium chloride contains both

Both may react to form a white precipitate.

ions:

ions:

Second observation:

"The white precipitate obtained and reacted with [dilute] HCl to give [colorless] gas bubbles."

The carbon dioxide gas from the reaction between and dilute HCl reacts with lime water (saturated calcium hydroxide solution in water) to form the white-colored, insoluble salt calcium carbonate . The precipitate will turn the lime water milky.

In summary,

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the answer to this question is 3.