Important MCQs of Chapter 1 Class 12 Chemistry

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XI MCQs on Mole Concept with Explanatory Answers

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    MCQs on Unit # 1… Mole Concept Set 1   1.   Which of the following contains the least numbers of molecules? (a) 1 g of H 2                                           (b) 4 g of O 2                                          (c) 2 g of N 2                           (d) 3 g of Cl 2   Explanation; (Answer; d) Substance containing least number of moles would have least number of molecules. Here 3g of Cl 2 contains least number ...
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Model Test Questions XII Chemistry Chapter # 1 Chemistry of Representative Elements

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Short Question Answers from Textbook 1. Give reason for the following: ▶ Ionization energy decreases from top to bottom in s-block elements. ▶ Boiling points of halogens increase down the group in the periodic table. ▶ Gallium has smaller atomic radii than aluminium despite being below the aluminium in group IIIA. ▶ Electronegativities of alkali metals decrease from Li to Cs. ▶ Acidity of hydrogen halides increase from HF to HI. ▶ Fluorine is the strongest oxidizing agent.   2. What is flame test? Mention the colour flame of alkali metals.   3. What is meant by a diagonal relationship? Mention three pairs of representative elements that show diagonal relationship.   4. Discus the group trend of ionization energy in group IIIA and IVA of the periodic table.   5. Write down four properties of beryllium that show its unique behaviour in group IIA.   Short Question Answers from Past Papers  Q1. Write down three points to show the...
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Derivation of Radius, energy, energy difference, frequency, wave no, and wavelength of the nth Bohr’s Orbit for Hydrogen-Like Atoms

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  Derivation of  Radius of the n th  Bohr’s Orbit for Hydrogen-Like Atoms Assumptions for s imple a tom To derive an expression for radius, consider a hydrogen atom (or hydrogen-like atoms such as He + , Li 2+ , Be 3+ , B 4+ , C 5+ ) with atomic number equal to z consisting of a single electron with charge –e and mass m revolving around the nucleus of charge +Ze (+e is charge of proton) with a tangential velocity v in the orbit whose radius is r. Now revolving electron is being acted upon simultaneously by the following two types of forces ; (i) Electrostatic force of Attraction / Centripetal Force According to Coulomb’s law, the electrostatic force of attraction (F e ) between the nucleus of charge ‘+Ze’ and electron of charge ‘–e’ separated by a distance ‘r’ is given by: Where ‘K’ is proportionality constant. It is equal to 1/4 π ε o r 2 Hence attractive force between nucleus and electron can be written as...
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