1- Where are isotopes of the same element having different atomic masses placed in the periodic

table?

2-Iit is desired to obtain an erect image of an object, using an concave mirror of focal length 20cm.

(i) What should be the range of the distance of object from the mirror?

(ii) Will the image be bigger or smaller than the object?

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

3-(a) What are the main reasons why human beings are over-exploiting the forests?

(b)What are the effects of damages?

(c)Names the different measures taken up for the conservation of forests?

4- a) Define homologous series of organic compounds. Mention any two characteristics of

homologous series.

b) Name the compound formed on heating ethanol at 443k with excess of conc.H2SO4.

c) Describe a chemical test to distinguish between ethanol and ethanoic acid.

5-:a)Why do we classify elements ?

b) What were the two criteria used by Mendeleev in creating his periodic table?

c) In Mendeleev‘s periodic table, why was there no mention of noble gasses like helium, neon

and argon?

d) Why did Mendeleev leave some gaps in his periodic table?

e) Would you place the two isotopes of chlorine, Cl-35 in different slot because of their different

atomic masses or in the same slot because their chemical properties are the same ? Justify your

answer.

6-Pollination may occur without fertilization but fertilization will not take place without

pollination. Give reason .

Q1.. According to Modern periodic table, the isotopes are not placed in different places , rather they are considered to have a single place because according to modern periodic law, atomic no. is more accurate property than the atomic mass and so the elements have been arranged in order of increasing atomic number. Hence, the isotops are placed in same position.

Q2. (a) Homologous series:-  A homologous series is defined as a group of structurally similar organic compounds in which all the members contain the same physical and chemical properties and any two successive members of which differ by a -CH₂ group. The individual members are called homologous and the phenomenon is called homology.

Characteristics:

1. Each homologous series can be represented by a general formula. For ex; C_nH_2n+1COOH is the general formula of carboxylic acid series.

2.All the members of given homologous series possess same functional group.

3.The chemicals and physical properties are nearly similar and changes according to rise in atomic mass.

(b) when ethanol is heated at 447 K with excess of conc. H₂SO₄ it gives Ethylene CH₂=CH₂

First of all it gives ethyl hydrogen sulphate and finally produces ethylene.

CH₃CH₂-OH + H₂SO₄ ---> CH₃CH₂OSO₃H (ethyl hydrogen sulphate)

CH₃CH₂OSO₃H ---> CH₂=CH₂ 

(c).  Ethanol reacts with Na- metal to give hydrogen gas with effervescence but ethanoic acid does not give this test.

2CH₃CH₂OH + 2Na à 2CH₃CH₂ONa + H₂(gas)

Also, the eheanol has a sweet smell while ethanoic acid smells as vinegar .

Q3. (a) Since, there are nearly 114 elements are known and we need to study them all.

But, it is impossible to remember all the physical and chemical properties of each and every element so we need to classify them on the basis of some similar characteristics so that, if we study one element we would be able to understand the properties if others too.

(b) Mendeleev, took the formulas of hydride and oxide of elements and the order of their atomic weight in order to create his periodic table.

(c). Mendeleev created his periodic table in about 1869 but the noble or inert gases were not known at that time.

These noble gases were discovered in about 1900. Thus, Mendeleev did not placed noble gases in periodic table, but later they were included in his original periodic table.

(d) Since Mendeleev arranged the elements in order of increasing atomic weiht and at that time only 63 elements were discovered , so he found some atomic weight and properties vacant and left some place for the elements to be discovered matching to the atomic weights and properties. 
Later, he proposed some elements and which were found correct after discovery. So, Mendeleev left some gap in the periodic table.

(e) Acording to Modern periodic law, the atomic no. is more fundamental property of an element than the atomic mass as the atomic no. is the no. of electrons and we know that all the chemical roperties are based on electrons. Since, the isotops of Cl-35 have similar atomic no. and they differ in atomic masses only so we should place them in same place because in classification, the elements with similar properties are placed together.