Find out, from Table 10.3, the medium having highest optical density. Also find the medium with lowest optical density.

Material medium	Refractive index	Material medium	Refractive index
Air	1.0003	Canada Balsam	1.53
Ice	1.31
Water	1.33	Rock salt	1.54
Alcohol	1.36
Kerosene	1.44	Carbon disulphide	1.63
Fused quartz	1.46
Turpentine oil	1.47	Ruby	1.71
Benzene	1.50	Sapphire	1.77
Crown glass	1.52	Diamond	2.42

     Table 10.3 Absolute refractive index of some material media

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Outline a project which aims to find the dominant coat colour in dogs.

Draw the structure for the following compounds.                

       (i)    Ethanoic acid             (ii)   Bromopentane*
       (iii)  Butanone                   (iv)   Hexanal.

*Are structural isomers possible for bromopentane?

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

How is the sex of the child determined in human beings?

(a)  What property do all elements in the same column of the Periodic Table as boron have in common?
(b)  What property do all elements in the same column of the Periodic Table as fluorine have in common?

Calculate the number of electrons constituting one coulomb of charge.

What is an homologous series? Explain with an example.

Why is variation beneficial to the species but not necessarily for the individual?

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

What evidence do we have for the origin of life from inanimate matter?

How do we detect the smell of an agarbatti (incense stick)?

Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

What is an homologous series? Explain with an example.

How are fats digested in our bodies? Where does this process take place?

What are alloys?

Why does dry HCl gas not change the colour of the dry litmus paper?