NSTSE Sample Paper Solutions Class 12 PCB

UNIFIED COUNCIL A n I S O 9 0 0 1 : 2008 C e r t i f i e d O r g a n i s a t i o n Test Assess Achieve NATIONAL LEVEL SCIENCE TALENT SEARCH EXAMINATION Solutions for Class : 12_PCB BIOLOGY 5. (A) Aurochs was the extinct wild ox of 1. (C) Condition reflexes are also known as Europe. acquired reflexes because these PHYSICS reflexes are first learned (experienced) 6. (A) A parallel plate capacitor is charged and adn then cause reflex action. the battery used for charging is then Conditional reflexes were first disconnected. The voltage across the demonstrated by Russian scientist, plates increases. Pavlov on dogs. This type of reflex is 7. (C) The magnitude of the e.m.f. across the controlled by both brain and pinal cords. secondary of a transformer depends 2. (B) Biological Oxygen Demand (BOD) is a upon. measure of polluting organic matter (a) the magnitude of the emf applied across present in a sample of water. BOD is the primary. higher in polluted sewage water and is (b) the number of turns in the primary and connected with both microbes and the secondary. organic matter. When larger amount of sewage is dumped into water, the BOD NS  e = .e 2 p S NP2 will increase. 3. (A) Mosses and ferns require presence of 8. (B) There will be no loss of energy if the water for fertilization that is why they potential of spheres is the same i.e., if are found in moist and shady habitat. V q  Q q Q 4  0 R (or) r R , qR = Qr  Other similarities between both these 4  0 r groups are: 9. (C) If the plane of the coil makes an angle (i) Development of embryo occurs within with the magnetic field, the magnitude the archegonium. of the torque exerted on it is given by (ii) Presence of heterogenous alternation of  = nIAB sin  . For the given value of generation. , when A is doubled  value doubles. (iii) presence of cuticle. 10. (A) A thermistor is a heat sensitive resistor, whose value varies appreciably with (iv) Presence of multicellular sex organs temperature more so than in standard with a jacket of sterile cells. resistors. Therefore, its temperature (v) Presence of multicellular sporangia. coefficient of resistivity should be high. Thermistors are usually made up of (vi) Presene of flagaellated male gametes. metal oxides. 4. (B) Being dioecious, a dog cannot be self- CHEMISTRY fertilized. 11. (B) In the addition of HCN to carbonyl group of a ketone, microphic nitrite or cyanide website : www.unifiedcouncil.com 1

ion attacks the carbonyl atom with 15. (C) Amorphous solids do not melt. They simultaneous transfer of  -electrons to simply soften on heating, and gradually the oxygen atom of the carbonyl group. begin to flow on further heating. These solids are, therefore considered as super 12. (A) The ideal conditions for the manufacture cooled liquids. of H2SO4 by contact process are low temperature, high pressure and high CRITICAL THINKING concentration of reactants. 16. (D) 13. (B) Benzoic acid in benzene exists as dimer. 17. (D) 14. (A) Two ‘  ’ Amino acids on condensation between COOH and NH2 groups form 18. (C) dipeptide which further reacts with other amino acids forming polypeptides which 19. (B) are called proteins when there are 100 20. (C) or more amino acids. website : www.unifiedcouncil.com 2