10 Science Solved Sample Paper 4 – Page 3
Question: 12. The electronic configurations of the four elements A, B, C and D are given below: 
A – 2, 1
B – 2, 2
C – 2, 8, 2
D – 2
(1). Which amongst these elements belong to same group? Write chemical name of any one of these.
(2). Which amongst these elements belong to same period? Write chemical name of any one of these.
(3). Which amongst these is not a metal? Write its chemical name.
- B and C; Beryllium/Magnesium
- A and B; Lithium/Beryllium
- D; Helium
Question: 13. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. 
Question: 14. List any four methods that can be adopted by human-beings for contraception. Explain in brief how the health and prosperity of a family is affected, if these methods are adopted by the husband or the wife. 
Answer: Four contraceptive methods – (i) Mechanical barriers, (ii) Contraceptive pills, (iii) Loop or Copper – T, surgical methods etc.
Effects: (i) Frequent or unwanted pregnancies are avoided, (ii) Helps in protecting health of women, (iii) Parents can give more care to their child/children.
Question: 15. ‘Twinkling of starts is due to atmospheric refraction.’ Explain this statement with the help of a diagram and state the reason why planets do not twinkle. 
Question: 16. Why can’t two magnetic field lines cross each other? Draw the magnetic field lines (including field directions) of the magnetic field due to a long straight solenoid. What important property of this field is indicated by this field line pattern? Name any two factors on which the magnitude of the magnetic field due to this solenoid depends. 
Answer: If two magnetic field lines will cross each other, then there will be two direction of magnetic field at the point of crossing, which is not possible in a magnetic field. The field around a solenoid is like that of a Bar magnitude of the current passing through the solenoid.
With the help of a labelled circuit diagram describe an activity to illustrate the pattern of the magnetic field lines around a straight current carrying long conducting wire.
(1). Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor.
(2). Is there a similar magnetic field produced around a thin beam of moving: (a) alpha particles and (b) neutrons? Justify your answer.
Question: 17. (a).Write the electron dot structure for calcium and oxygen. The atomic numbers of calcium and oxygen are 20 and 8 respectively.
(b). Show the formation of calcium oxide by the transfer of electrons.
(c). Ionic compounds are high melting solids. Give reason. 
(c). Ionic compounds have high melting point, as their oppositely charged ions are strongly held together by strong electrostatic force of a attraction.