Board Paper of Class 10 2018 Science (SET 3) - Solutions

• Question 1
  A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F₁ progeny? VIEW SOLUTION

• Question 2
  Write the energy conversion that takes place in a hydropower plant. VIEW SOLUTION

• Question 3
  If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer. VIEW SOLUTION

• Question 4
  A compound 'X' on heating with excess conc. sulphuric acid at 443 K gives an unsaturated compound 'Y'. 'X' also reacts with sodium metal to evolve a colourless gas 'Z'. Identify 'X', 'Y' and 'Z'. Write the equation of the chemical reaction of formation of 'Y' and also write the role of sulphuric acid in the reaction. VIEW SOLUTION

• Question 5
  (a) Name one gustatory receptor and one olfactory receptor present in human beings.
  
  (b) Write a and b in the given flow chart of neuron through which information travels as an electrical impulse.
  
  $\begin{array}{ccccccc}\boxed{ \mathrm{Dendrite} }& \to & \boxed{ \mathrm{a} }& \to & \boxed{ \mathrm{b} }& \to & \boxed{ \mathrm{End} \mathrm{point} \mathrm{of} \mathrm{Neuron} }\end{array}$ VIEW SOLUTION

• Question 6
  Show how would you join three resistors, each of resistance 9 Ω so that the equivalent resistance of the combination is (i) 13.5 Ω, (ii) 6 Ω?
   

  OR

  (a) Write Joule's law of heating.
  (b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V. VIEW SOLUTION

• Question 7
  State the laws of refraction of light. Explain the term 'absolute refractive index of a medium' and write an expression to relate it with the speed of light in vacuum.

  OR

  
  What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens. VIEW SOLUTION

• Question 8
  Name the hormones secreted by the following endocrine glands and specify one function of each:
  (a) Thyroid               (b) Pituitary                (c) Pancreas VIEW SOLUTION

• Question 9
  Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival – the one reproducing asexually or the one reproducing sexually? Give reason to justify your answer. VIEW SOLUTION

• Question 10
  (a) List the factors on which the resistance of a conductor in the shape of a wire depends.
  
  (b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity? Give reason?
  
  (c) Why are alloys commonly used in electrical heating devices? Give reason. VIEW SOLUTION

• Question 11
  What is a dam? Why do we seek to build large dams? While building large dams, which three main problems should particularly be addressed to maintain peace among local people? Mention them. VIEW SOLUTION

• Question 12
  Students in a school listened to the news read in the morning assembly that the mountain of garbage in Delhi suddenly exploded and various vehicles got buried under it. Several people were also injured and there was traffic jam all around. In the brain storming session the teacher also discussed this issue and asked the students to find out a solution to the problem of garbage. Finally they arrived at two main points -one is self management of the garbage we produce and the second is to generate less garbage at individual level.
  
  (a) Suggest two measures to manage the garbage we produce.
  (b) As an individual, what can we do to generate the least garbage? Give two points.
  (c) List two values the teacher instilled in his student in this episode. VIEW SOLUTION

• Question 13

  (a) Why are most carbon compounds poor conductors of electricity?

  (b) Write the name and structure of a saturated compound in which the carbon atoms are arranged in a ring. Give the number of single bonds present in this compound.
   

  VIEW SOLUTION

• Question 14
  2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of a strong acid.

  
  OR

  
  The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses. VIEW SOLUTION

• Question 15
  Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. VIEW SOLUTION

• Question 16
  (a) A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
  
  (b) Why do stars twinkle ? Explain.
   

  OR

  
  (a) Write the function of each of the following parts of human eye :
  (i) Cornea (ii) Iris (iii) Crystalline lens (iv) Ciliary muscles
  
  (b) Why does the sun appear reddish early in the morning? Will this phenomenon be observed by an astronaut on the Moon ? Give reason to justify your answer. VIEW SOLUTION

• Question 17
  (a) Mention any two components of blood.
  (b) Trace the movement of oxygenated blood in the body.
  (c) Write the function of valves present in between atria and ventricles.
  (d) Write one structural difference between the composition of artery and veins.
   

  OR

  
  (a) Define excretion.
  (b) Name the basic filtration unit present in the kidney.
  (c) Draw excretory system in human beings and label the following organs of excretory system which perform following functions :

  (i) form urine.
  (ii) is a long tube which collects urine from kidney.
  (iii) store urine until it is passed out.

  VIEW SOLUTION

• Question 18
  (a) Write the function of following parts in human female reproductive system :

  (i) Ovary    (ii) Oviduct    (iii) Uterus

  
  (b) Describe in brief the structure and function of placenta. VIEW SOLUTION

• Question 19
  (a) State Fleming's left hand rule.
  
  (b) Write the' principle of working of an electric motor.
  
  (c) Explain the function of the following parts of an electric motor.

  (i) Armature (ii) Brushes (iii) Split ring

  VIEW SOLUTION

• Question 20
  (a) Write the steps involved in the extraction of pure metals in the middle of the activity series from their carbonate ores.
  (b) How is copper extracted from its sulphide ore? Explain the various steps supported by chemical equations. Draw labelled diagram for the electrolytic refining of copper. VIEW SOLUTION

• Question 21
  (a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation or all the three attempts.
  (b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.
  State Modern periodic law. VIEW SOLUTION