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Archive for the ‘CBSE – IX’ Category

Science – IX

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Chemistry – IX – CBSE STRUCTURE OF THE ATOM Important Questions Q. 1. How can you say that matter is electrical in nature ? Ans.:- (i) By rubbing ebonite rod with cat skin we see that ebonite rod is negatively charged and cat’s skin is positively charged. (ii) A glass rod gets a positive charge [...]

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Science – IX

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Chemistry – IX – CBSE STRUCTURE OF THE ATOM Important Questions Q. 36. State the model of an atom proposed by J. J. Thomson. Ans.:-               fig.4.5/ p. 104. J. J. Thomson proposed that : (i) An atom contains positively charged sphere embedded in it like seeds embedded in watermelon. (ii) The negative and positive charges [...]

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Science – IX

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Chemistry – IX – CBSE STRUCTURE OF ATOM Important Questions. Q. 78. How are the electrons arranged outside the nucleus ? Ans.:- Bohr and Bury stated the following rules for the distribution of electrons around the nucleus : (i) Electrons are revolving around the nucleus in different orbits or shells. These shells are called energy [...]

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Science – IX

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Chemistry – IX – CBSE STRUCTURE OF ATOMS Important questions :- Q. 90. What are valence electrons ? Explain with examples. Ans.:-  Valence electron is the number of electrons present in the outermost orbit of an atom . Examples : Elements Atomic number Electronic configuration Valence electron Boron 5 2, 3 3 Oxygen 8 2, [...]

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Science – IX

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Chemistry – IX – CBSE Structure of atom Important questions : Q. 97. What is atomic number ? How the definition of an element is improved by this concept ? Ans.:- The number of protons present in the nucleus of an atom is equal to the atomic number of an element. As the atom as [...]

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Science – IX

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Chemistry – IX – CBSE Structure of Atoms Important Questions Q. 127. Define isotope with suitable example. Ans.:- Atoms of the same element with the same atomic number but different atomic masses, are called isotopes. This suggests that number of protons in the isotopes are same but number of neutrons are different in their nuclei. [...]

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Science – IX

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Science – IX – CBSE Laws of chemical combinations Q. 1. What is law of conservation of mass ? Ans.:- Law of conservation of mass :- It states that mass can neither be created nor destroyed. For example if we take x gram of lead nitrate solution in a beaker and add y gram of [...]

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Science – IX

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Science – IX – CBSE Important Questions Arrangement of atoms in molecules : Atoms of a molecule are chemically bonded in a definite pattern and definite spatial arrangement depending on the nature of chemical bonding between them. Q. 31. Differentiate between a molecule and a compound. Ans.:- Usually molecules are formed by the combination of [...]

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Science – IX

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Science – IX – CBSE Molecular formula Important Questions Q. 65. The calcium salt of a hypothetical anion Z has the molecular Ca3Z2. Find the valency of Z and write the molecular formula of the aluminium salt of Z. Ans.:- Valency of Z = – 3 Valency of Al = 3 Formula of aluminium salt [...]

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Science – IX

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Science – IX – CBSE Mole Concept Important Questions Q. 80. Explain the term ‘mole concept’. Ans.:- A mole of any species (atoms, molecules, ions, particles) is that quantity which will have a mass equal to its atomic mass or molecular mass in grams. The number is 6.022 × 1023 and is fixed. Thus a [...]

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