Earth, Moon, and the Sun — Science STD 7 — Question

Why is it important to learn from failed experiments?

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Why is vegetative propagation a preferred method of asexual reproduction?

Use a torch and a ball in a dark room to show how only half of the Earth receives sunlight. Describe your observation and also draw the diagram.

Mention any two features that are seen in boys and girls each to distinguish them from each other at puberty.

Nitrogen is an essential nutrient for plant growth. But farmers who cultivate pulse crops like green gram, bengal gram, black gram, etc. do not apply nitrogenousfertilisers during cultivation. Why?

The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?

Explain the term lateral inversion.

A food stall owner was preparing dough for making bhaturas. He added a pinch of yeast and sugar to the dough and left it in a warm place. After few hours, the dough had risen. There was a sour smell too. What would have happened if the dough was kept in the refrigerator, soon after it was prepared?