Important Questions Test: Acids Bases & Salts - Class 7 MCQ

• China rose indicator is like a magic potion that helps us know if a liquid is sour or sweet. When China rose meets something sour, like lemon juice, it turns the color to dark pink. But if it meets something sweet, like soda water, it changes to green.

• So, when China rose indicator meets acidic solutions, it turns them dark pink (magenta). When it meets basic solutions, it changes them to green. That's why the statement is True!

Since phenolphthalein turns pink in a basic solution and remains colourless in acidic and neutral solutions, if there's no change observed upon its addition, the solution must be either acidic or neutral.

The correct answer is C: Hydrochloric acid.

Explanation:

• Bases are substances that can accept hydrogen ions (protons) or more commonly produce hydroxide ions (OH⁻) in solution.


• Magnesium hydroxide, calcium hydroxide, and sodium hydroxide are all bases because they produce hydroxide ions when dissolved in water.


• Hydrochloric acid (HCl) is an acid, not a base. It donates hydrogen ions (H⁺) in solution, which is characteristic of acids.

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Acid rain is created when substances like carbon dioxide, sulphur dioxide, and nitrogen dioxide mix with raindrops in the air. These substances make the rain harmful and can damage buildings, plants, and animals.

Milk of magnesia is an antacid.
Antacids are medicines that counteract (neutralise) the acid in your stomach to relieve indigestion and heartburn

Apple juice is acidic in nature due to the presence of organic acids, such as malic acid, which lower its pH. Unlike soap solution, which is basic, and slaked lime, which is also basic, apple juice has a pH below 7, making it acidic. This acidity is what gives apple juice its characteristic tart taste.

Neutral solutions are substances that do not change the color of either red or blue litmus paper. This means they are neither acidic nor basic.

• The curd is produced due to the presence of reaction between lactic acid bacteria and the milk protein casein.
• When milk sugar or lactose undergoes fermentation, the product obtained is lactic acid.

• When you put a drop of soap solution on turmeric paper, the paper turns red.
• This change in color happens because of a chemical reaction between the soap solution and the turmeric, showing that soap is a type of substance called a base.
• So, when soap solution comes in contact with turmeric paper, it changes the color to red.