A student placed a pinch of solid sodium hydrogencarbonate on a strip of red litmus paper. He found that the colour of red litmus paper strip :
(1)turned green (2)turned blue
(3)turned violet (4)did not change
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Correct answer: (4) did not change

Explanation: Solid sodium hydrogencarbonate does not (H⁺ or OH^- ions) changes the colour of litmus paper. As there is no presence of ions, hence the colour of the litmus paper does not change.