NCERT Exemplar Problems Class 9 Science

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NCERT Exemplar Problems class 9 Science

Class:9
Subject:Science
Contents:NCERT Exemplar Problems

NCERT Exemplar Problems class 9 Science Solutions

NCERT Exemplar Problems class 9 Science Solutions of all MCQ, short and long answers are given below to free download in Hindi and English Medium.



CHAPTER 1: MATTER IN OUR SURROUNDINGS

CHAPTER 2: IS MATTER AROUND US PURE

CHAPTER 3: ATOMS AND MOLECULES

CHAPTER 4: STRUCTURE OF THE ATOM

CHAPTER 5: THE FUNDAMENTAL UNIT OF LIFE

CHAPTER 6: TISSUES

CHAPTER 7: DIVERSITY IN LIVING ORGANISMS

CHAPTER 8: MOTION

CHAPTER 9: FORCE AND LAWS OF MOTION

CHAPTER 10: GRAVITATION

CHAPTER 11: WORK AND ENERGY

CHAPTER 12: SOUND

CHAPTER 13: WHY DO WE FALL ILL

CHAPTER 14: NATURAL RESOURCES

CHAPTER 15: IMPROVEMENT IN FOOD RESOURCES




Chapter 1: Matter in Our Surroundings – Main Points

Matter is made up of small particles.
The matter around us exists in three states— solid, liquid and gas.
The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.
The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.
The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.
The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa.
Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.
The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.
Evaporation causes cooling. Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point. Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.




What are the important topic in Chapter 2 Is Matter Around Us Pure?
  • mixture contains more than one substance (element and/or compound) mixed in any proportion.
  • Mixtures can be separated into pure substances using appropriate separation techniques.
  • A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute.
  • The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution/solvent.
  • Materials that are insoluble in a solvent and have particles that are visible to naked eyes, form a suspension. A suspension is a heterogeneous mixture.
  • Colloids are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light. Colloids are useful in industry and daily life. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium.
  • Pure substances can be elements or compounds. An element is a form of matter that cannot be broken down by chemical reactions into simpler substances. A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.
  • Properties of a compound are different from its constituent elements, whereas a mixture shows the properties of its constituting elements or compounds.

What are main point on Chapter 3: Atoms and Molecules?
  • During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is known as the Law of Conservation of Mass.
  • In a pure chemical compound, elements are always present in a definite proportion by mass. This is known as the Law of Definite Proportions.
  • An atom is the smallest particle of the element that can exist independently and retain all its chemical properties.
  • molecule is the smallest particle of an element or a compound capable of independent existence under ordinary conditions. It shows all the properties of the substance.
  • chemical formula of a compound shows its constituent elements and the number of atoms of each combining element.
  • Clusters of atoms that act as an ion are called polyatomic ions. They carry a fixed charge on them.
  • The chemical formula of a molecular compound is determined by the valency of each element.
  • In ionic compounds, the charge on each ion is used to determine the chemical formula of the compound.
  • Scientists use the relative atomic mass scale to compare the masses of different atoms of elements. Atoms of carbon-12 isotopes are assigned a relative atomic mass of 12 and the relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom. The Avogadro constant 6.022 × 10^23 is defined as the number of atoms in exactly 12 g of carbon-12.
  • The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.
  • Mass of 1 mole of a substance is called its molar mass.

Give the keywords for Chapter 4: Structure of the Atom?
  • Credit for the discovery of electron and proton goes to J.J. Thomson and E.Goldstein, respectively.
  • J.J. Thomson proposed that electrons are embedded in a positive sphere.
  • Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.
  • Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model.
  • Neils Bohr’s model of the atom was more successful. He proposed that electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive.
  • J. Chadwick discovered presence of neutrons in the nucleus of an atom. So, the three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutronsElectrons are negatively chargedprotons are positively charged and neutrons have no charges. The mass of an electron is about 1/2000 times the mass of an hydrogen atom. The mass of a proton and a neutron is taken as one unit each.
  • Shells of an atom are designated as K,L,M,N,….
  • Valency is the combining capacity of an atom. The atomic number of an element is the same as the number of protons in the nucleus of its atom.
  • The mass number of an atom is equal to the number of nucleons in its nucleus.
  • Isotopes are atoms of the same element, which have different mass numbers.
  • Isobars are atoms having the same mass number but different atomic numbers.
  • Elements are defined by the number of protons they possess.



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