Early and modern theories

Correct answer: C. It explains planet formation through a gas-dust disk and accretion without depending on a rare passing star

The modern model matches normal physical processes and observations better. In exams, write the difference between a rare event and an evidence-based model.

Correct answer: A. It gave a direction to explain solar system origin through natural gaseous matter and gravitational concentration

Kant's idea came before modern evidence but started a natural explanation. In exams, remember both contribution and limitation.

Correct answer: D. Because planet formation was better explained through a detailed sequence of flat disk, condensation, and accretion

Laplace discussed rings, but the modern model explains processes more clearly. In exams, identify the difference between old idea and modern sequence.

Correct answer: B. Both assume gradual joining of small bodies to develop larger planetary bodies

Growth of small building bodies is important in both. In exams, also remember the difference in source material.

Correct answer: C. It is difficult to explain orderly same-direction planetary orbits from matter pulled by a passing star

The tidal theory cannot satisfactorily explain ordered planetary motion. In exams, treat orbital order as a major limitation.

Correct answer: A. Angular momentum of the same rotating protoplanetary disk

Bodies formed from one rotating disk can be arranged in similar direction and plane. In exams, write angular momentum and disk together.

Correct answer: D. Temperature and distance influenced the composition of inner rocky and outer gaseous-icy planets

Beyond the frost line, icy materials could remain and outer planets grew larger. In exams, connect temperature, distance, and material.

Correct answer: B. High temperature and young Sun's solar winds did not allow light gases to remain

Near the Sun, light gases were reduced and rocky material dominated. In exams, explain inner planets through temperature and material availability.

Correct answer: A. After icy cores formed in cold regions, stronger gravity accumulated more gases

In the cold outer region, both icy solids and gases were more available. In exams, connect gas giants with cold region and greater mass.

Correct answer: C. Because it indicates recession of distant galaxies and expansion of the universe

Red shift is a sign of motion in space. In exams, write it as observational evidence of expansion.

Correct answer: B. The universe had an early hot phase followed by expansion

Background radiation indicates an early hot state and red shift indicates expansion. In exams, link both evidences with the Big Bang.

Correct answer: D. To keep the average density of the universe same despite expansion

The steady state theory imagined creation of new matter during expansion. In exams, remember average density and continuous creation together.

Correct answer: A. Cosmic microwave background radiation

This radiation was considered a remnant of the early hot universe. In exams, remember it as support for the Big Bang and a challenge to steady state.

Correct answer: C. Big Bang, early matter, galaxies and stars, solar nebula

First the universe and matter formed, then large structures, and later the solar system formed. In exams, remember the large-to-small sequence.

Correct answer: A. They later became a broad cosmic basis for stars and solar nebula material

Light elements were early material in broad cosmic evolution. In exams, place Earth in the wider cosmic sequence.

Correct answer: B. Accretion increased Earth's mass and differentiation formed density-based internal layers

Accretion builds the planetary body and differentiation forms its internal structure. In exams, write these processes with order and function.

Correct answer: B. Density-based heavy materials moving to form the core

Heavy materials such as iron and nickel moved to the center and helped form the core. In exams, connect metal, density, and core.

Correct answer: C. It allowed heavy and light materials to separate according to density

In molten state, materials remained mobile and differentiation became possible. In exams, treat melting as a condition for layer formation.

Correct answer: D. Heat increase, partial melting, and possibility of differentiation

Both heat sources played a role in Earth's internal development. In exams, connect heat sources with differentiation.

Correct answer: A. Outgassing brought gases from Earth's interior and supplied material for the early atmosphere

Gas release produced water vapour and other gases. In exams, connect the early atmosphere with internal gases.

Correct answer: B. Because widespread oxygen-producing photosynthetic life had not yet developed

Free oxygen increased through later biological development. In exams, do not treat the early atmosphere as the same as the present atmosphere.

Correct answer: C. Earth cooled, water vapour condensed, rain and water bodies formed

The hydrosphere includes all water on Earth, such as oceans, rivers, lakes, groundwater and water vapour. In the early history of Earth, the planet was extremely hot. As its surface and atmosphere cooled, water vapour could change into liquid water through condensation. The condensed water fell as rain, and over long periods it collected in low areas to form oceans and other water bodies. Therefore, the order must begin with cooling, followed by condensation, rainfall and collection.

Option C gives the correct sequence: Earth cooled, water vapour condensed, rain fell, and water bodies formed. Option A reverses the basic order because stable surface water could not form before the necessary cooling. Option B is incorrect because red shift is an observation related to motion and distance in astronomy, not the process that directly formed Earth’s water. Option D does not describe the accepted sequence. The answer follows a clear cause-and-effect chain.

Correct answer: D. A stable surface formed for water retention and development of outer spheres

The solid crust provided a base for hydrosphere and later surface development. In exams, connect crust with Earth's outer development.

Correct answer: A. The early solar system was impact-active and Earth also underwent large impacts

The giant impact idea links Moon origin with the active state of early Earth. In exams, treat it as a modern explanation.

Correct answer: C. It is based on known decay of radioactive isotopes

The rate of radioactive decay provides a basis for age estimation. In exams, connect Earth's age with scientific evidence.