A student mixed some soil with water in a beaker and allowed it to settle. He filtered the contents of the beaker and obtained a clear filtrate. When he put a few drops of the filtrate on the pH paper, the pH paper turned yellowish orange. Which of the following should the student put on this pH paper so that it may change its colour to greenish-blue?
(1) NaHCO3 solution
(2) HCI solution
(3) Vinegar solution
(4) Common salt solution
Correct answer: (1) NaHCO3 solution
Explanation: The yellowish-orange colour of the pH paper indicates it is an acid. So, in order to convert the yellowish-orange colour to greenish-blue, the student needs to add a base in it. From the given options, the sodium bicarbonate solution is a base.
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