CBSE Class 11 Geography — NCERT Solutions

Correct option: (b) Erathosthenese

The Greek scholar Eratosthenes (276–194 BC) was the first to use the word 'Geography' (Greek: Geo = Earth, Graphos = description/writing). He is therefore regarded as the father of Geography.

Correct option: (c) Plain

A plain is a naturally formed landform created by geological and geomorphic processes, making it a physical (natural) feature. Ports, roads, and water parks are all man-made (cultural/human-made) features.

Correct Answer: (c) 8°4'N – 35°6'N

Justification: The mainland of India extends from 8°4'N latitude in the south (Kanyakumari) to 35°6'N latitude in the north (near Kashmir). This is the standard latitudinal extent cited for India's territory. Option (b) gives an incorrect northern limit of 37°6'N, and option (a) gives a slightly wrong southern limit of 8°41'N. Hence, option (c) is correct.

Correct Answer: (a) Bangladesh

Justification: India shares a land boundary of approximately 4,156 km with Bangladesh, which is the longest land frontier India shares with any single neighbouring country. China comes second with about 3,488 km, followed by Pakistan (~3,323 km) and Myanmar (~1,643 km). Hence, Bangladesh shares the longest land frontier with India.

Correct Option: (c) 4.6 billion years

Scientific evidence based on radioactive dating of meteorites and lunar rocks establishes that the earth is approximately 4.6 billion years (4,600 million years) old. 13.7 billion years refers to the estimated age of the universe (Big Bang), not the earth.

Correct Option: (b) Differentiation

Differentiation is the process by which the earth separated into layers (core, mantle, crust) based on density — it is related to the internal structure of the earth, not directly to the formation or modification of the atmosphere. Solar winds drove away the primordial atmosphere; degassing released gases from the interior to form the secondary atmosphere; and photosynthesis added oxygen to the atmosphere.

Correct Answer: (c) 10° Channel

Justification: The 10° Channel (so named because it lies along the 10° North latitude) separates the Andaman Islands (to the north) from the Nicobar Islands (to the south). The 11° Channel, on the other hand, separates the Little Andaman from Car Nicobar.

Correct Answer: (c) Surface waves

Surface waves (also called L-waves or Long waves) travel along the surface of the Earth. They have the largest amplitude and the slowest velocity among all earthquake waves. Because they travel along the Earth's surface and cause the ground to move both vertically and horizontally, they produce the maximum damage to structures and are therefore the most destructive of all earthquake waves.

Correct Answer: (d) The Damodar

The Damodar river was known as the 'Sorrow of Bengal' because it used to frequently flood the plains of West Bengal, causing widespread destruction of life and property. It flows through Jharkhand and West Bengal and was notorious for its devastating floods before the Damodar Valley Corporation (DVC) was established to control them.

Correct option: (c) Abraham Ortelius

Abraham Ortelius, a Dutch map maker, was the first to suggest in 1596 that the continents of Europe, Africa, and America might have once been joined together, based on the matching coastlines he observed on maps. Alfred Wegener later formalised this idea into the Continental Drift Theory in 1912.

Correct answer: (c) North-Eastern monsoon

Justification: By the beginning of winter (October–November), the South-West monsoon retreats from most of India. However, the North-Eastern monsoon (also called the retreating monsoon) picks up moisture while crossing the Bay of Bengal and causes rainfall along the Coromandel Coast (Tamil Nadu). This is why Tamil Nadu receives most of its rainfall during winter, unlike the rest of India.

Correct Option: (d) Erosion

Gradational processes are those that tend to reduce or level the relief of the earth's surface. They include both denudation (weathering + erosion) and deposition. Among the given options, Erosion is a gradational process because it wears down and removes surface material, thereby reducing relief. Diastrophism and Volcanism are endogenic (internal) processes, while Deposition, though part of gradation, is the constructional side; Erosion is the classic example of a gradational (denudational) process.

Correct Option: (b) Deciduous forest

Sandalwood (Santalum album) is a well-known tree found in tropical moist and dry deciduous forests of India, particularly in Karnataka and Andhra Pradesh. Deciduous forests shed their leaves during the dry season, and sandalwood is a classic example of a commercially valuable deciduous tree species.

Correct option: (a) Youth stage

Justification: In the youth stage of landform development, rivers have steep gradients and high velocity. The dominant process is vertical (downward) cutting, which deepens the valley rapidly. Lateral erosion and widening become significant only in later stages.

Correct answer: (c) Assam

Assam experiences floods most frequently among the given options. The Brahmaputra river and its numerous tributaries overflow their banks almost every year during the monsoon season, inundating large parts of the state. Assam's low-lying topography, heavy rainfall, and the silt-laden Brahmaputra make it the most flood-prone state in India.

Correct Option: (b) Nitrogen

Nitrogen constitutes approximately 78.08% of the total volume of the atmosphere, making it the most abundant gas. Oxygen comes second at about 20.95%, while Argon and Carbon dioxide are present in much smaller quantities.

Correct Option: (c) 23.5° N

Justification: 21st June is the Summer Solstice in the Northern Hemisphere. On this date, the Earth's axial tilt causes the sun to be directly overhead (at zenith) at noon over the Tropic of Cancer, which is located at latitude $23.5°$ N. This is the northernmost latitude at which the sun can ever be directly overhead.

Correct option: (c) 900 mb

Justification: Atmospheric pressure decreases with increasing altitude. As a general rule, pressure decreases by approximately 100 mb for every 1 km rise in altitude. Therefore, at 1 km above the surface where pressure is 1,000 mb, the pressure will be approximately $1,000 - 100 = 900$ mb.

Correct Option: (a) Water vapour

Water vapour is the most important constituent of the atmosphere for human beings because it is the source of all forms of precipitation (rain, snow, hail, etc.), regulates temperature by absorbing terrestrial radiation, and is essential for the hydrological cycle that sustains life on Earth.

Correct Option: (c) Mean monthly temperature of all the months more than 18°C

Justification: Koeppen's 'A' type (Tropical Humid Climate) is defined by the criterion that the mean monthly temperature of every month of the year is more than 18°C. This distinguishes it from other climate types. High rainfall in all months is a feature of only the 'Af' sub-type, not the entire 'A' group.

Correct Option: (b) Hydration

Justification: The hydrological cycle involves the continuous circulation of water through evaporation, condensation, and precipitation. Hydration is a chemical process (water combining with another substance) and is not a component of the hydrological cycle.

Correct Option: (c) wave

Waves are the upward and downward (oscillatory) movement of ocean water. In a wave, water particles move in a circular orbit — rising and falling — while the wave form itself travels forward. Tides are caused by gravitational pull, and currents are horizontal movements of water, so neither fits the description of upward and downward movement.

Correct option: (d) All organisms

Biodiversity refers to the variety of all living organisms on Earth — including animals, plants, microorganisms, and fungi. Conservation of biodiversity is important for all organisms because every species plays a role in maintaining ecological balance and the health of ecosystems that support all life forms.