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When you add sodium hydrogen carbonate to acetic acid in a test tube, a gas liberates immediately with brisk effervescence. Name this gas. Describe the method of testing this gas. CBSE- class10- Science 20151 AnswerWrite the number of covalent bonds in the molecule of propane, C3H8 . CBSE- class10- Science 20151 AnswerThe first trophic level in a food chain is always a green plant. Why? CBSE- class10- Science 20152 AnswerName the life process of an organism that helps in the growth of its population. CBSE- class10- Science 20151 AnswerWrite the number of covalent bonds in the molecule of ethane. CBSE- class10- Science 20151 AnswerList six specific characteristics of sexual reproduction. CBSE- class10- Science 20151 AnswerWhat is meant by scattering of light? Use this phenomenon to explain why the clear sky appears blue or the Sun appears reddish at sunrise. CBSE- class10- Science 20151 AnswerList two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed. CBSE- class10- Science 20151 AnswerWhat are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. CBSE- class10- Science 20151 AnswerExplain the following: (a) Speciation (b) Natural Selection CBSE- class10- Science 20151 AnswerDraw the electron - dot structure for ethyne. A mixture of ethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mix ture of ethyne and air for this purpose? CBSE- class10- Science 20151 AnswerList four points of significance of reproductive health in a society. Name any two areas related to the reproductive health which have improved over the past 50 years in our country. CBSE- class10- Science 20151 AnswerWhat is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it. CBSE- class10- Science 20151 AnswerList two main causes of the pollution of water of the river Ganga . State how pollution and contamination of river water prove harmful for the health of the people of neighbouring areas. CBSE- class10- Science 20151 AnswerWhere is DNA found in a cell? CBSE- class10- Science 20151 AnswerWhat will be the amount of energy available to the organisms of the 2 nd trophic level of a food chain if the energy available at the first trophic level is 10,000 joules? CBSE- class10- Science 20151 AnswerDifferentiate between biodegradable and non - biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non - biodegradable waste, for saving the environment. CBSE- class10- Sci1 AnswerWhat are the hydrocarbons? Distinguish alkanes from alke nes and each of them from alkynes giving one example of each. Also draw the structure s of each compound cited as example to justify your answer . CBSE class10 Science 20161 Answer( a ) What is fragmentation in organisms ? Name a multicellular organism which reproduces by this method. ( b ) How does regeneration take place? Why is this process not possible in all animals? CBSE class10 Science 20161 AnswerList two physical and two chemical properties of acetic acid which a student can test in the school laboratory. CBSE class10 Science 20161 Answer