Four students a, b, c, and d measured the pH values of water, lemon juice, and sodium bicarbonate solution. What is the correct decreasing order of the pH value? 

An acid is a species that donates protons and a base is one that accepts protons or donates hydroxide ions.

pH is a scale that indicates whether the substance is an acid, base or neutral.

• For an acidic substance, pH <7.
• For a neutral substance, pH = 7.
• For a basic substance, pH>7.

Now, Sodium carbonate is a strong base and has pH>7. And lemon juice contains citric acid and thus its pH is <7.

Water is a neutral liquid, thus its pH = 7.

Thus, the correct order of pH will be;

Sodium bicarbonate>water>lemon juice.

Hence, the correct option is (A).