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

ions and ions.

Both may react to form a white precipitate.

ions:

might react with hydroxide ions to form the white-colored, weakly-soluble base magnesium hydroxide . might also react with carbonate ions to form the white-colored, insoluble salt magnesium carbonate, .

ions:

ions might react with silver ions to form the white-yellowish insoluble salt silver chloride .

Second observation:

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

Indeed will react with dilute HCl, but no gas will be formed: . reacts with dilute HCl to produce the colorless gas carbon dioxide : .Silver chloride does not react with dilute HCl.

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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And a) oxygen i believe