a) Sate three conditions necessary for combustion. b) What beneficial role do micro-organisms play in the life of human beings? c) Write equation of following reaction- a. Sulphur dioxide gas with water b. Zinc and sodium hydroxide solution. d) You want to buy a few summer dresses, which fabric would you choose cotton or nylon and why? e) When the gold ornaments are sent to the jewellers for polishing them always loses a small amount of weight. Explain how does this happen. f) Why friction is called a necessary evil? g) Why do farmers cultivate plants of pea family? h) What is crop rotation? Mention its advantages. i) What do you understand by streamlining? Name a few machines which use streamlining to reduce friction. j) Why does the nose of some people start bleeding at higher altitudes? Die
Answers
Answer:
A. Three things are required in proper combination before ignition and combustion can take place---Heat, Oxygen and Fuel. There must be Fuel to burn. There must be Air to supply oxygen. There must be Heat (ignition temperature) to start and continue the combustion process.
B. For example, each human body hosts 10 microorganisms for every human cell, and these microbes contribute to digestion, produce vitamin K, promote development of the immune system, and detoxify harmful chemicals. And, of course, microbes are essential to making many foods we enjoy, such as bread, cheese, and wine.
C. 1. SO2 + 2 H2S → 3 S + 2 H2O. The sequential oxidation of sulfur dioxide followed by its hydration is used in the production of sulfuric acid.
2. Sodium hydroxide reacts with zinc and water to form sodium zincate and hydrogen gas. Zn(s)+2NaOH(aq)+2H2O(l)→Na2Zn(OH)4(aq)+H2(g).
D. Cotton is the best material for summers as it alows air to have contact to our body, it has light weight and does not let sweat to flow easily and absorbs most of it. Wearing nylon in summers may develop rashes on your skin and irritate you too much but cotton clothes do no harm to you.
E. To polish a gold ornament, it is dipped in a liquid called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting the environment of aqua regia, the outer layer of gold dissolves and the inner shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewellery.
F. Frictional force causes a lot of losses in general upkeep and wear and tear of machinery. ... But almost all crucial tasks cannot be carried out without the presence of friction. Basic activities like walking and writing on a surface are possible due to friction. Hence it is considered as a necessary evil.
G. The bacterium is Rhizobium is found in the root nodules of leguminous plants such as peas. It lives in symbiotic association withplants and fixes the atmospheric nitrogen in leguminous plants. This increases the fertility of the soil. Hence, farmers cultivate plants belonging to the legume family.
H. By rotating your crops, it helps to shift the composition of the soil. The change in the soil helps to ward off diseases in your crops. A healthier crop means a better yield. Changing locations of your crops helps to reduce the localization of insects.
I. A few machines which use streamlined shape to reduce friction are - Aeroplanes, Ship, Boat, Rockets, Missiles, Cars
J. High altitude – as altitude increases, the availability of oxygen decreases, making the air thinner and drier. The dryness can cause the nose to bleed.
Explanation:
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