Title Science X (Series DAA1B 3) For QR Code.pdf ✅

Shiv Das CBSE BOARD PAPER – 2024 (Series: DAA1B/3) S-3 Or (b) Solenoid is used to magnesite a piece of magnetic material when used as a core in the coil/solenoid. Solenoid Battery Key Soft iron core 26. Decomposers are the microorganisms that break down complex organic substances (dead remains and waste products of organism) into simpler organic substances that go into the soil and are used up once more by the plants. Consequences of their absence. (i) If there were no decomposers, then the dead bodies of plants and animals would keep lying as such. The elements of which plant and animals bodies are made, would never be returned to their original pools like soil, air and water. In that case, the cycling process of life and death would be disrupted. (ii) All the nutrients present in soil, air and water would soon be exhausted and evolution of life would come to an end. SECTION C 27. (a) Zinc oxide is an amphoteric oxide because it reacts with acid as well as with bases to form salt and water ZnO (s) + 2 HCl (aq) ZnCl2 (aq) + H2O (l) Acid Salt ZnO (s) + 2 NaOH (aq) Na2ZnO2 (aq) + H2O (l) bare Sodium Zincate (Salt) (b) Sodium metal reacts vigorously with oxygen (of air) and catches fire and starts burning when kept open in the air. Thus sodium metal is stored under kerosene oil to prevent its reaction with oxygen and moisture. (c) When a metal reacts with dilute nitric acid then hydrogen gas is not evolved because nitric acid is a strong oxidising agent. So as soon as hydrogen gas is formed in the reaction between a metal and dilute nitric acid, the nitric acid oxidises this hydrogen to water. 28. (a) (i) Mercury is a less reactive metal, it is extracted by the reduction of its oxides by heat alone. When mercury oxide is heated at about 300oC, it gets reduced to form mercury metal 2 HgO (s) Heat → Reduction 2 Hg (l) + O2 (g) (ii) Copper is less reactive metal which is self reduced by heating its sulphide ore in air Cu2S + 3O2 Roasting → Cu2O + 2 SO2 Sulphide ore (from air) When good amount of Cu2S is converted into copper oxide then the supply of air is stopped, the copper oxide so formed reacts with copper oxide and gets reduced to copper. Cu2S + 2 Cu2O → Heat 6 Cu + SO2 (iii) Sodium which is highly reactive under electrolytic reduction of its molten chlorides or oxides as the bonding between sodium and oxygen is very strong. Or (b) (i) Silver gradually turns black due to the formation of a thin silver sulphide layer on its surface by the action of hydrogen sulphide gas present in air. (ii) When copper remains in damp air for a considerable time, then copper reacts slowly with carbon dioxide and water of air to form a green coating of basic copper carbonate on its surface. 2Cu(s) + H2O(g) + CO2 + O2 Cu(OH)2 + CuCO3(s) (Copper (Copper) Hydroxide) Corbonate) (iii) When an iron object is left in damp air for a considerable time, it gets covered with a red-brown flaky substance called rust because iron reacts with oxygen and moisture of the air to form hydrated iron (iii) oxide Fe2O3. x H2O.
Shiv Das S-4 Shivdas Board Exams Question Bank (Science X) 29. Most plants secure their water and minerals from their roots. Water and minerals are transported through xylem cells from the soil to the leaves. The xylem cells of roots, stem and leaves are interconnected to form a conducting channel. The root cells take ions from the soil. This creates a difference between the concentration of ions of roots and soil. Therefore, there is a steady movement of water into xylem. An osmotic pressure is formed and water and minerals are transported from one cell to the other due to osmosis. The continuous loss of water takes place due to transpiration. 30. (a) The two constituents of Central Nervous System (CNS) are Brain and Spinal cord. Brain is protected by a bony box in the skull called cranium. While spinal cord are covered by the vertebral column. Both the brain and spinal cord are surrounded by three membranes called meninges which help to protect them from injuries. The space between the meninges is filled with a Cerebra-spinal fluid which protects the brain and the spinal cord from mechanical shocks. Or (b) Limitations of electrical impulses. (i) The impulse can move only in one direction i.e., it has unidirectional flow. (ii) The electrical impulses are quite short acting. The message is only sent in the presence of the stimulus. 31. Phenomenon is Tyndall effect. The scattering of a beam of light is called the Tyndall effect. Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In a dense forest, the mist contains tiny droplets of water, which act as particles of colloid dispersed in air. Similarly, when a beam of light enters a smoke filled room through a small hole, its path becomes visible to us because tiny dust particles present in the air of room scatter the beam of light all round the room and when this scattered light enters our eyes, we can see the beam of light. Dependence of colour of light on size of particles. • When white sunlight falls on relatively larger particles like (dust particles etc.) present in the atmosphere it scatters the light as such due to which the scattered light also appears white. • The extremely small particles such as air molecules present in the atmosphere scatter mainly the blue light present in the white sunlight. 32. A fuse is a safety device having a short length of a thin, tin plated copper wire having low melting point, which melts and breaks the circuit if there is an overflow of current. An electric fuse works on the heating effect of current. A fuse wire is connected in series in the electric circuits. • In an Electric heater, P = 3 KW = 3000 W and V = 220 Volts Electric circuit rating = 5 A As we know, P = VI ⇒ I = P 3000W V 220 V ∴ = I = 13.6 A Current drawn by the electric heater is 13.6 A which is very high because the fuse in the circuit is only of 5 ampere capacity. When the 13.6 A current flows through the 5A fuse, the fuse wire will get heated too much. Thus it melts and breaks the circuit 33. (a) Ohm’s law states that the electric current, through a conductor, is directly proportional to the potential difference across its two ends when, other physical conditions like temperature, etc., remain constant. V  I or V I = Constant = R or V = IR 123 1 111 R RRR p =++ for parallel combination (b) R R R X× ×Y Resultant of two parallel resistors 1 1 1 11 2 R RR R R + =+= = ′  R′ = R 2 ...(i) Total resistance of the circuit, Rp = R + R′ (series) Rp = R + R 2 ...[From (i) ⇒ Rp = 2R R 2 +  Rp = 3R 2