4. List any two human activities that lead to an increase in the carbon dioxide content of air.
5. Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why? How does the speed of sound in air vary with rise in density of the medium?
6. The volume of 50 g of a substance is 20 cm. If the density of water is 1g/cm, will the substance float or sink? 7. What are polyatomic ions? Give any two examples. 8. Archimedes could find the purity of a king’s crown using buoyancy. How? 9. a. If an element M has mass number 27 and atomic number 13, how many neutrons does its atom contain? b. Define Avogadro’s constant. Give its value. 10. (a) Name any two green house gases. (b) What causes global warming? 11. Give two examples each of biodegradable and non-biodegradable pollutants. 12. Write two points of difference between gymnosperms and angiosperms. 13. List any two characteristics of division Pteridophyta that shows they are the most advanced cryptogams.
14. a. Draw a diagram depicting low pitched sound and high pitched sound. b. When a person uses deodorant spray, the other person standing at a distance would hear the sound of spraying first and the fragrance of spray would reach him later. Why so? 15.
(a) How do you define mechanical work? (b) Name and define SI unit of work? (c) What do you mean by positive and negative work? Give example.
16. Explain the working and application of a SONAR. 17. State any three postulates of Dalton’s atomic theory. 18. Calculate the number of molecules of sulphur present in 16 g of solid sulphur. 19. Give two examples of each of the following: a. Diseases which spread through air. b. Diseases which spread through water. c. Diseases which spread through insect. 20. What precautions can you take in your school to reduce the incidence of infectious diseases? Mention any three points. 21. List any two benefits of classification. Why bryophytes and pteridophytes grow in moist and shady places? 22. Explain, how HIV-AIDS virus affects and damages our body? What is an antibiotic?
23. (a) State the law of conservation of energy. (b) Name the type of energy possessed by the following: (i) stretched slinky (ii) a speeding car (iii) flowing water (iv) stretched rubber band. (c ) An object of mass 50 kg is raised to a height of 600 cm above the ground. What is its potential energy? (g = 10 m/s) Or (a) Define kinetic energy. Give examples. (b) Obtain an expression for the kinetic energy of an object of mass ‘m’ and possessing a velocity ‘v’. 24. (a) Chlorine...