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Ques 2: The above reaction is an example of a:              Fe 2  O 3  + 2 Al → Al 2   O 3  + 2 Fe (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction. Ans 2: (d) The given reaction is an example of a displacement reaction.                                                             

Ques 1: Which of the statements about the reaction below are incorrect?              2 P b O + C → 2 P b + CO (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced. (i) (a) and (b) (i i) (a) and (c) (i i i) (a), (b) and (c) (i v) all Ans 1: (i) (a) and (b)                                                                                                          

Ques : Conservation of momentum in a collision between particles/bodies can be understood from (a) Conservation of energy (b) Newton’s second law only (c) Newton’s first law only (d) Both Newton’s second and third law Ans : (d) Both Newton’s second and third law If there is no external force acting on a system (called isolated) of constant mass, the total  momentum of the system remains constant(no change) with time. For a two system of particles in absence of any external force by law of conservation of linear  momentum. Important point: We should not confuse with the system and the individual particles. As total external force on the system of both particles is zero but force acts on individual particles.  Law of conservation of linear momentum is independent of frame of reference(ground level or at some height) while linear momentum depends on frame of reference. 

Ques: What are the environmental consequences of using the fossil fuels? Suggest some steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.  Ans: Environmental consequences of using fossil fuels are: (i) They are the largest emitters of greenhouse gases such as sulphur dioxide, carbon dioxide and methane. (ii) Extraction of conventional fuels threatens the ecological balance in some areas. (iii) These fuels can cause environmental problems due to pollution. Steps to minimize the pollution are : (i) The dependency on fossil fuels should be reduced by switching to any other sources of energy. (ii) The judicious use of energy by avoiding the wastage can reduce environmental problems.  (iii) Regular servicing of energy conversion devices should be done in order to maintain their efficiency. Unit 14 (Sources of Energy) (iv) We should focus on developing the technology that should make the energy conversion devices much more effici

Ques: Write two different ways of harnessing energy from ocean. Ans: Tidal energy and Ocean thermal energy  can be harnessed from ocean.

Ans:  There is a need to harness the non-conventional sources of energy because: (i) fossil fuels are present in limited amount and are depleting fast. (ii) burning of fossil fuels causes a lot of air pollution.

Ques: Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C. Ans: 

Ques: Match the important chemicals given in Column (A) with the chemical formulae given in Column (B). Ans: 

Ques: A student prepared the solutions of (i) an acid and (ii) a base in two different beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since, both the solutions are colourless, how will she distinguish between the two of them? Ans: Add phenolphthalein (which is a indicator) to a portion of each solution in separate test tube. If it turns pink, then, the beaker contains base whereas if it remains colourless, it's an acid. If phenolphthalein is not available, pH paper can also be used. Acid will turn pH paper red, base will turn pH paper blue.

Ans: Egg-shell is made up of calcium carbonate( Ca CO 3) which will react with  HNO 3  to form  C 2 (g) and  H 2 (l) along with calcium nitrate.  Ca CO 3  +   HNO 3  →   Ca( NO 3 ) 2 +   CO 2   +   H 2 O

Ans: Ant sting contains methanoic acid (HCOOH) (formic acid). Its chemical formula is HCOOH. The common method to get relief from it is to apply paste of (baking soda) on it.

Ans: Dry HCl(hydrochloric acid) gas will have no effect on litmus paper. Moistened  NH 3  gas will turn red litmus blue. Curd, carbonated soft drink, lemon juice will turn blue litmus red. Soap solution will turn red litmus blue.

Ques: Match the acids given in Column (A) with their correct source given in Column (B). Ans.(a) —> (iv)         (b) —> (iii)          (c) —> (ii)          (d) —> (i) Lactic acid is present in curd,milk,etc. ; acetic acid is generally present in vinegar, citric acid is present in orange, lemon and oxalic acid is generally present in tomato.

Ques 1: A Mendelian experiment consisted of breeding tall pea(matar) plants bearing violet flowers with short pea plants bearing white flowers. The progeny of all bore violet flowers, but almost half  of them were short. This suggests that the genetic make-up of the tall parent can be depicted as   (a) TTWW (b) TTww (c) TtWW (d) TtWw Ans 1: (c) The genetical make-up of the tall parent can be depicted as TtWW .  Since all the progeny of pea plant bore violet flowers, it means that all the tall plants are having violet flowers has W W genotype for violet flower colour.   Since the progeny is both tall tall and short, the parent plant was not a pure tall plant. Its genotype must be T t.   Therefore, the cross involved in the given in the question is                        TtWw × ttww                                    ↓                        TtWw − ttww Therefore, half of the progeny is tall, but all of them is having violet flowers. Ques 2: An example of homologous o

Ques: Find out the following in the electric circuit given in figure: (a) Effective resistance of two 8 Ω resistors in the combination, (b) Current flowing through 4 Ω resistor, (c) Potential difference across 4 Ω resistance, (d) Power dissipated in 4 Ω resistor,  (e) Difference in ammeter readings, if any. Ans: (a) Effective resistance, the two 8 Ω resistors in parallel, R = 8×8 / 8+8    = 4 (b) equivalent resistance = 4 + R = 8 Ω So, current through 4 Ω = I = V/R = 8/8 = 1A   (c) Potential difference = V = IR = 1×4 = 8 V (d) Potential dissipated = I²R = I² × 4 = 4 V (e) No difference, since the ammeters are connected in series and the same amount if current pass through them, so the reading of both the ammeters will be same.