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CBSE Class 10 Science Solved Question Paper 2014

Short Answer Type

21.

The elements Be, Mg and Ca each having two electrons in their outermost shells are in periods 2, 3, and 4 respectively of the modern periodic table. Answer the following questions, giving justification in each case:

(i) Write the group to which these elements belong.

(ii) Name the least reactive element.

(iii) Name the element having a largest atomic radius.

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22.
A carboxylic acid (molecular formula C₂H₄0₂) reacts with an alcohol in the presence of an acid catalyst to form a compound 'X'. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid C₂H₄0₂. Write the name and structure of

(i) carboxylic acid, (ii) alcohol and (iii) the compound 'X'.

The chemical name of given carboxylic acid is ethanoic acid. When ethanoic acid reacts with the acid in the presence of an acid such as sulphuric acid as a catalyst to produce the ester, (ethyl ethanoate).

$stack CH subscript 3 COOH with Ethanoic space acid below space plus stack CH subscript 3 minus CH subscript 2 minus OH space with Ethyl space alcohol below rightwards harpoon over leftwards harpoon from KMnO subscript 4 to straight H subscript 2 SO subscript 4 left parenthesis catalyst right parenthesis of space stack CH subscript 3 COOCH subscript 2 CH subscript 3 with Ethyl space ethanoate below space plus stack straight H subscript 2 straight O with Water below$

i) Carboxylic acid = Ethanoic acid
ii) alcohol = Ethyl alcohol
iii) Compound X = ethyl ethanoate

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23.

Define the term ‘structural’ isomerism'. Explain why propane cannot exhibit this property. Draw the structures of possible isomers of butane, C₄H₁₀ .

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24. A concave mirror of focal length 15 cm can form a magnified, erect as well as inverted image of an object placed in front of it. Justify this statement stating the position of the object with respect to the pole of the mirror in both the cases for obtaining the images.

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25.

A student wants to project the image of a candle flame on a screen 90 cm in front of a mirror by keeping the flame at a distance of 15 cm from its pole.

(a) Suggest the type of mirror he should use.

(b) Determine the linear magnification in this case.

(d) Draw ray diagram to show the image formation in this case.

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26.

Draw a ray diagram to show the path of the refracted ray in each of the following cases:

A ray of light incident on a concave lens is:

(i) passing through its optical centre.

(ii) parallel to its principal axis.

(iii) directed towards its principal focus.

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27.

A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram.

Trace it on your answer sheet and show the path of the emergent beam as observed on the screen DE.

(i) Write the name and cause of the phenomenon observed.

(ii) Where else in nature is this phenomenon observed.

(iii) Based on this observation, state the conclusion which can be drawn about the constituents of white light.

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