Class 7 Science Chapter 4 MCQ

Lemon water is acidic in nature. Acids do not turn all indicators red e.g. china rose indicator turns to dark pink (magenta) when acidic compound is added to it. Common salt and water both are neutral. Hence, have no effect on litmus.

Making solution of acid and water evolve heat. Acid should be added to water dropwise.

Turmeric paste is yellow in acidic solution and turns red in basic solution.

Instead of these she should take, an antacid (milk of magnesia) which is a base and neutralize the acidity. Milk of magnesia contains a base magnesium hydroxide which reacts with the acids and cures indigestion.

Phenolphthalein remains colour-less in acidic solution but turns pink in basic solution.

Here, all the statements are correct. Hence, your answer will be option [D].

Organic matter (called manure or compost) releases acids which neutralize the excess bases present in the soil and reduce its basic nature.

The soil may be acidic or basic naturally. The excessive use of fertilizers in the fields also makes the soil too acidic. When the soil is too acidic, it is treated with base such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralize the excess acid present in the soil and reduces its acidic nature. In the soil is too basic, then decaying organic matter (called manure or compost) is added it. The decaying organic matter releases acid which neutralize the excess bases present in the soil and reduces its basic nature. Hence, your answer will be option [D].

Litmus is a mauve (purple) colour pigment obtained from Lichens. It turns red when added to acidic solution and blue when added to a basic solution.

Here all the statements are correct. Hence, your answer will be option [D].

Neutralization reaction is a chemical reaction between acid and base to produce salt and water. It cannot be reversed.

Tooth decay is caused by the presence of an “acid”. Sodium Hydroxide turns red litmus blue. Here only option [B] is correct. Hence, your answer will be option [B].

As an example, to understand: methyl orange and phenolphthalein used as indicator. In acidic solution, methyl orange gives red colour but in basic solution it gives yellow colour. In acidic solution, phenolphthalein is colourless but in basic it gives pink colour. Thus, the change of colour in acid and a base depends on the type of indicators.

When litmus is added to a basic solution it turns “blue”. Rest of all statements are correct. Hence, your answer will be option [D].

Bases turn china rose indicator to “green”. Rest of all statements are correct. Hence, your answer will be option [C].

Curd contains lactic acid and vinegar contains acetic acid. Lime water, soap and milk of magnesia are basic substances and grapes contain tartaric acid.

Phenolphthalein indicator is synthetic (man-made), acid-base indicator. Rest of all statements are correct. Hence, your answer will be option [A].

Citric acid is present in citrus fruits such as lemon and oranges. And tartaric acid is present in tamarind.

Here all the statements are correct. Hence, your answer will be option [D].

Ammonium hydroxide or ammonia solution is found in window cleaners. Rest of all statements are correct. Hence, your answer will be option [D].

Sodium hydroxide and potassium hydroxide are dangerous bases which can burn our skin. They must be handled very carefully.

Calcium Hydroxide, ammonium hydroxide and sodium carbonate are weak base but their solution are unsafe to drink. Magnesium hydroxide is a very weak base which is safe to drink. It is used in milk of magnesia and other indigestion mixtures.

Red litmus gives red colour in lemon juice which cannot be seen because red color mix with red litmus paper. Rest of all options are correct. Hence, your answer will be option [D].

Acid and base participate in neutralization reaction and produce salt and water.

Antacids are a group of mild bases which have “no” toxic effects on the body. Rest of all statements are correct. Hence, your answer will be option [B].