CBSE Class 9 Social Science — NCERT Solutions

Any other two plates from the map with their matching continents and ocean are also correct.

There is a clear correlation: most earthquakes and volcanoes occur along plate boundaries. The map shows that the areas with frequent earthquakes and volcanoes match the edges of tectonic plates, especially around the Pacific Ocean in the Ring of Fire.

The atmosphere is a mixture of gases. The two main gases are nitrogen and oxygen. In smaller amounts, it also contains carbon dioxide, argon, helium, neon, krypton, xenon, ozone, hydrogen, and it has water vapour and tiny dust particles. Water vapour usually ranges from 0.1% to 0.4%.

The atmosphere has five main layers, and each affects Earth in a different way. The troposphere is the lowest layer and is the most important for life because it contains the air we breathe, most water vapour, clouds, and nearly all weather phenomena like rain, fog, and hail. The stratosphere lies above it and contains the ozone layer, which protects life by filtering harmful ultraviolet rays from the Sun; it is also good for flying aeroplanes because the air is calm and cloud-free. The mesosphere is the layer where temperature decreases with height and most meteors burn up. The thermosphere absorbs X-rays and short-wave ultraviolet radiation, so its temperature rises sharply; it also helps radio transmission and is where auroras occur. The exosphere is the outermost layer, with very thin air, where light gases like hydrogen and helium escape into space. Together, these layers protect Earth, control weather, and support life.

Before civilisation, humans lived as hunter-gatherers. They moved from place to place in search of food, used stone tools, lived in caves or open camps, and later formed temporary settlements near rivers and lakes. In the Palaeolithic period they hunted animals, gathered plants, and depended directly on nature. Over time, they developed tools, techniques, and other forms of technology to survive changing environments.

Before writing was invented, humans communicated through speech, gestures, symbols, paintings, and engravings. Early humans also decorated cave walls and rock shelters with paintings and used symbols and motifs on pottery and seals. Such symbolic communication helped them express ideas before written language developed.

Before 1000 CE, Indian society and state developed from kin-based groups like jana and kula into territory-based units such as janapadas and mahājanapadas. Over time, some regions grew into larger kingdoms and empires like the Mauryas, Guptas, Satavāhanas, Pallavas, and later the Cholas. Society was organised through customs, varṇa, jāti, family, gotra, occupations, and assemblies such as sabhā and samiti. State administration became more complex, with kings, ministers, officers, provinces, districts, villages, taxes, armies, and councils. The chapter also shows continuity through ideas like dharma, chakravarti samrāṭ, and ethical governance.

It is important because in a democracy the people are the source of all power. If power rests with the people, then the government must work for them and remain answerable to them. This protects freedom, equality, justice, and rights, and prevents rulers from becoming arbitrary or above the law.

Elections are essential because they are the main way in which citizens exercise their right to vote and choose those who will make decisions on their behalf. In a democracy, rulers must be chosen periodically, so people can give or withdraw their mandate. Elections also make representatives accountable to the people. Without regular elections, the people cannot change non-performing leaders, and democracy becomes weak.

Economics deals with choice in the presence of limited resources and unlimited wants. It studies how individuals, enterprises, governments, and societies use scarce resources efficiently to satisfy needs and wants, and the opportunity cost of those choices.

The demand for goods and services is influenced by price, income of the consumer, prices of related goods (substitutes and complements), taste and preference, population size and composition, seasonality, future price expectations, and diminishing marginal utility. Demand also depends on purchasing power, meaning people must be willing and able to buy.

The supply of goods and services is influenced by price, prices of related goods, number of sellers in the market, technology, future expectations, and changes in weather, input costs, availability of resources, and other disruptions. In general, higher prices raise supply and lower prices reduce it.