Q] Choose one option for each
1) Which of the following chemicals has affected the ozone layer?
a) Carbon compound b)  NO_{2}
c) Chlorofluoro carbon d) Carbon tetra chloride]

2) Which of the following substance is used in the hydrogenation of vegetable oil?
a) Finely divided nickel b) Platinised gauze
c)Finely divided platinum d) Finely divided iron

3) Digestion in human body is an example of which type of reaction?
a) Displacement reaction b) Decomposition reaction
c) Double decomposition reaction d) Combination reactions

4) In the experiment, a burning matchstick is held near the mouth of the test tube containing hot HgO. It burns brightly. Why?
a) Mercury oxide decomposes into mercury and hydrogen
b) No change in the compound takes place
c) Heat is available from the flame
d) Oxygen gas is evolved

5) Which of the following statement is true for sodium atoms and sodium ions?
a) They are chemically same b) They have same number of protons
c) They have identical number of electrons d) They form covalent bonds

6) When an ionic bond is formed?
a) The combining atoms gain electrons
b) The combining atoms lose electrons
c) A metallic element reacts with nonmetallic element
d) Two metallic elements reacts

7) Which is the electronic configuration of chlorine atom?
a) 2,8,7 b) 2,8,8 c) 2,8,5 d) 2,8,4

8) What is the percentage of sulphur in a molecule of sulphuric acid?
a) 40 b) 35 c) 65 d) 32.65

2

Answers

2014-09-07T13:20:17+05:30
1) c) Chlorofluoro carbon  and d) Carbon tetra chloride (both cause destruction to ozone layer)
2) a) Finely divided nickel 
3) b) Decomposition reaction
4) d) Oxygen gas is evolved
5) b) They have same number of protons
6) c) A metallic element reacts with nonmetallic element
7) a) 2,8,7
8) d) 32.65
2 3 2
ur welcone
EXPLANATION NEEDED
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2014-09-10T05:30:01+05:30

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1 Chlorofluoro carbon from greenhouse gases raises to the ozone layer high in the atmosphere. the flourine becomes free radical after decomposition by energy due to uv rays. free fluorine starts chain reaction to split Ozone molecule and reduces it.

2. Finely divided nickel powder acts as a catalyst during the hydrogenation of vegetables oils i.e, when carbon carbon double bonds are replaced by single bonds as some c - h bonds are formed.

3. Decomposition reaction as the food is split or broken down in to smaller components.
enzymes chemically break down the food in to smaller components. HCl and pepsin digest proteins and converts into polypeptides or amino acids.

4. Hg O decomposes into Hg and O in presence of light or heat and O2 helps burning of matchstick.

5. Na and Na⁺ one positive charge.  they have number of same protons, neutrons in the nucleus. Na becomes Na⁺ when an electron jumps out of the atom to some other atom.

6. a simple chemical compound M H is formed when M⁺ positive ion and H⁻ negative ion come together. One atom M loses electron and another H gains electron. Metals have tendency to lose electrons easily. non metallic elements have tendency to gain electrons.

7. 1s²  2s² 2p⁶ 3s² 3p5  as its atomic number = 17 = 17 electrons.    2,8,7
     fill in from 1st quantum number 1s orbital = 2 max.  total = 2
                   2nd quantum level:  2s orbital = 2 max   2p orbital = 6 max.   total = 8
                   3rd quantum:  3s orbital 2 max.  Now 5 remain for 3p, where 6 are max.
                   3rd quantum level: total 7

8. H₂ S O₄  = sulphuric acid or sulfuric acid.  want the percentage by WEIGHT.
         atomic weights of atoms: H = 2,  S = 32 ,  O = 16

        % of sulphur =  total weight of S atoms / total molecular weight  * 100
                           = 32 * 100 / (2*2 + 32 + 16*4) = 3200 / 100 = 32 %

2 5 2
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