Question

why does the salt become bluish in colur after squeezing lemon onto it​

Answer 1

because it contains iodine

Answer 2

Citric acid releases iodine ions from the salt. These iodine ions in presence of starch will result in a purple colored starch/iodine complex. ... Secondly, the salt may have a small amount of blue colourant added to it to give a "whiter"shade to the salt. When added lemon juice disolves this colourant from the salt.

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