Q] Choose one option for each and explain how it is correct. EXPLANATION NEEDED
1) 24 g of magnesium and 73 g of hydrochloric acid react chemically to give 2 g of hydrogen and X g of magnesium chloride. X g represents which of the following number?
a) 95 g b)92 g c) 85 g d)70 g

2) In the reaction of hydrogen sulphide and chlorine. What type of change takes place in hydrogen sulphide?
a) It is reduced. b) It is oxidized. c) It is neutralized. d) It is decomposed.

3) The electronic configuration of some of the elements is given below. Which of the following elements is chemically inert?
a) 2,4 b) 2,8,7 c) 2,8,8 d) 2,8,1

4) Which of the following gases has the smell of rotten eggs?
a) Carbon monoxide b) Nitrogen dioxide c) Hydrogen sulphide d) Sulphur dioxide

5) Why tamarind is used to clean brass vessels?
a) It has an organic acid which helps to dissolve any oxide formed on the surface
b) It makes vessel bright c) It is easily available d) It is very cheap

6) What does a pH value 7 indicate?
a) Alkalinity b) Acidity c) Neutral d) Cannot identify property

7) Which of the following gases is liberated when sodium bicarbonate is heated?
a) Hydrogen b) Carbon dioxide c) Oxygen d) Sodium oxide

8) Which of the following is not a copper alloy?
a) Brass b) Gun metal c) Nichrome d) German Silver

9) Which of the following is the ore of Aluminium?
a) Magnetic b) Bauxite c) Chalcopyrites d) Galena

10) This structural formula represents a molecule of which organic compound?
(for structural formula see the picture below)
a) Ethane b) Propane c) Ethylene d) Acetylene

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2014-09-10T18:53:34+05:30

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1.  Mg + 2 H Cl -> H₂ + Mg Cl₂

     Given 1 molar weight (24g) of Mg, 2 molar weight and they produce 1 mole of H₂ (2g) and one mole of Magnesium chloride - 95 g

2.    H₂ S + Cl₂ -> S + 2 H Cl    This is oxidation of the compound.

3.    1s²  2s² 2p⁶  3s² 3p⁶ - The orbitals are completely filled. no empty energy state  is left. So this element will be inert. it is argon.

4.  hydrogen sulfide has the smell of rotten eggs - smell of sulphur

5   tamarind contains tartaric acid

6.  pH = 7 implies  the solution is neutral. the ionic concentration of Hydrogen ions and hydroxide ions is same.

7.     2 Na H CO₃ ->  Na₂ CO₃ + H₂ O +  CO₂          carbon dioxide.

8    nichrome is an alloy of nickel and chromium

9    Bauxite is the ore of Aluminum - the main compound from which Al is extracted.

10 Ethyne or acetylene   H - C Ξ C - H

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