1)Why doesn't Oil Dissolve In Water ?
 
Water is the most commonly used solvent. Some substances such as salt and sugar dissolve easily but few other such as oils , fats , and many organic substances din't. We wonder why it is so. It is because of the scientific principle' Like dissolve Like'. It means that substances with similar types of molecules alone make solutions.
                   If a substance has to dissolve in water, its molecules must be capable of forming electrostatic bonds with the water molecules. Molecules of water are polar i.e. one side of each water molecule has a partial positive charge and the other side has a partial negative charge.When the molecules of another substance such as common salt ( Sodium chloride), having ionic or polar character are put in water they get dissolved in it readily. Polar water molecules are drawn to the charged sodium and chloride ions and form a cluster around them. Then the attraction between sodium and chloride reduces. They separate and spread through the water in the form of a solution.
                     Oil molecules do not dissolve in water because the bonds of oil molecules are different from those of the water molecules. The molecules of oil are usually much bigger in size and contain many more atoms than those of water. They have Co-valent bonds. Oil droplets floats on water because the force of attraction between water and oil molecules(adhesive force) is less than the force of attraction (cohesive force) between oil molecules. So the oil molecules do not spread in water , i.e, they do not dissolve in water.

2) Discovery of Australia :

Australia is the world's smallest continent we all know, but the largest island. Its total area is about 2967877 sq.mi . In the medieval times people talked about the existence of a 'large continent in the 'Southern Hemisphere'. But since no voyager had discovered, nobody could say anything with certainty, people wondered what it was like and whether it was inhabited or not. It was called ' The Unknown Southern Land'.
          In order to expand their commercial activities, Europeans had been seeking new lands during 16th century. Dutch were the first to visit Australia in 1606. Their ship called the 'Duyfken' anchored off northern Australia. Some of the ship's crew went ashore to refill their water casks. The fierce natives of the land had driven them away. The 'Duyfken' sailed away from there without exploring any other part of the continent. Dutch government had sent captain Abel Tasman in 1642 to explore more about this continent. He explored and stored lot of information about the northern coast of the continent. he also discovered an island which is now called Tasmania and explored New Zealand.
        Later in 1770 the English captain James Cook discovered the east coast of Australia and named it New South Wales. In 1788 the first English colony was established in the city of Sydney. Now the important question is who the first inhabitants of Australia were. It is believed about 20000 years ago , a race of dark - skinned curly haired natives, known as Tasmonoids, went from New Guinea and settled in what is now called Australia. At the same time  in australia ,another race, the Australoids, arrived from Southern India. These two races fought for land. In this fight Australoids drove away Tasmonoids. They settled at another place, which is now known as Tasmania. The Australia remained there and became the original settlers of Australia. 
                        Today Australia is one of among the highly developed continents of the world. Its inhabitants are self - sufficient in almost every respect of life. It has many peculiarities. Two - thirds of its land is desert. In this continent many peculiar animals and birds are found. Kangaroo is one of them. The beautiful black swan is also a common sight here. It is also a land of minerals besides its richness in gold,tungsten, manganese, cobalt, lead and zinc.

3) Who are Incas?
 
Incas Valley

Incas are an Indian people in South America who flourished between 1200 and 1533 AD. The Inca empire was centered in Cuzco in the Peruvian Andes. It covered from Qunto, Ecuador to the Rio Maule in Central Chile.
                     The Incas possessed remarkable powers of organization and united people from different areas, though many of them spoke different languages, into one closely knit society. The emperor had Supreme Power over his kingdom. He claimed to be the representative of the Sun-God and ruled by divine right. As both god and king, the emperor of Inca,led a highly organized ritualistic religious life. Although an absolute obedience was required, an early form of Socialism was followed. It was guided by the principle that the king was responsible for providing welfare to all people. The Incas developed an advanced society. Although they were not as skilled as the Aztecs in astronomy and mathematics, incas went far beyond them in engineering, architecture, textiles, ceramics and metal works. their skill in engineering and building overcame great obstacles of geography and climate. This is clearly seen even today in the remains of many cities, half - hidden in the Jungles and in the ruins of an extensive and highly developed system of roads.