What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)
Sulphur molecule exists as S8. Its dot structure is
Draw the structure for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
What is an homologous series? Explain with an example.
How would you name the following compounds?
(i) CH3 -- CH2 -- Br
(ii)
(iii)
What will be the formula and electron dot structure of cyclopentane?
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Why are carbon and its compounds used as fuels for most applications?
How many structural isomers can you draw for pentane?
Explain the mechanism of the cleaning action of soaps.
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Explain the formation of scum when hard water is treated with soap.
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the difference between a reflex action and walking?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Why should a magnesium ribbon be cleared before burning in air?
Define the principal focus of a concave mirror.
Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
What is meant by power of accommodation of the eye?
What are the differences between autotrophic nutrition and heterotrophic nutrition?
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and c
(iv) all
Besides gallium, which other elements have since been discovered that were left by Mendeléev in his Periodic Table? (any two)
Why is the use of iodised salt advisable?
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
A solution of a substance 'X' is used for whitewashing.
(i) Name the substance 'X' and write its formula.
(ii) Write the reaction of the substance 'X' named in (i) above with water.