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.

Phenolphthalein is a synthetic (man-made) indicator.

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

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

Indicator phenolphthalein gives “pink” colour with lime water because lime water is a base.

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

Here all the statements, which are related to indigestion, are correct. 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].

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

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

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.

Basic solution changes the turmeric indicator from yellow to red.

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

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].

Hydrochloric acid, sulphuric acid and nitric acid are strong acids. On the other hand, acetic acid, formic acid, citric acid, tartaric acid and carbonic acid are some examples of the “weak acid”. Rest of all 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.

Turmeric paste changes its colour from yellow to red when treated with a base. So, turmeric is an acid base indicator.

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.

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].