Interior structure of the earth

Correct answer: B. P waves can pass through liquid but S waves cannot

P waves travel in solids liquids gases while S waves do not travel in liquids. Exam tip: remember medium capacity of P and S waves.

Correct answer: A. Radius about 6371 kilometres and core from about 2900 kilometres depth

Earth radius is about 6371 kilometres and core begins around 2900 kilometres depth. Exam tip: remember radius and core boundary separately.

Correct answer: A. Liquid outer core

Motion of liquid metallic outer core is linked with Earth's magnetic field. Exam tip: connect magnetism with outer core.

Correct answer: B. Iron and nickel

The direct answer is B: the core is mainly composed of iron and nickel. Earth’s core is the deepest major internal layer. On the basis of composition, it is traditionally called NIFE, from Ni for nickel and Fe for iron. The outer core is liquid and the inner core is solid because of the enormous pressure, but both are mainly metallic and rich in iron, with nickel and smaller amounts of other elements. Option A is wrong because silica and alumina are associated with SIAL and the lighter continental crust, not the main composition of the core. Option B is correct because iron and nickel are the standard school-level chemical description of the core. Option C is wrong because oxygen and hydrogen are not the accepted main metallic composition of the core. Option D is wrong because ice and salt describe neither the hot, dense metallic core nor its physical conditions. The reasoning is: identify the deepest layer, recall the traditional term NIFE, expand it as nickel plus iron, and choose B. Memory cue: NIFE = Ni + Fe, so core = nickel and iron.

Correct answer: A. Where some seismic waves are not recorded

Shadow zone forms due to stopping or bending of waves. Exam tip: connect shadow zone with core evidence.

Correct answer: A. Refraction

Bending of a wave due to change of medium is called refraction. Exam tip: connect P wave path change with refraction.

Correct answer: A. They can show internal density differences

Gravity field is affected by local density distribution. Exam tip: treat gravity anomaly as a density clue.

Correct answer: A. They indicate presence and motion of metallic materials in core

Magnetic field is considered related to liquid metallic outer core. Exam tip: connect magnetic evidence with core.

Correct answer: A. Internal heat can affect mantle convection

Internal heat can produce slow movement in mantle material. Exam tip: connect mantle convection with internal heat.

Correct answer: A. Continental crust is generally thicker than oceanic crust

Crust is thicker in continental areas than in oceanic areas. Exam tip: remember continental crust as thicker.

Correct answer: A. They do not represent all depths and all layers

Volcanic materials are direct sources but give information from limited depths. Exam tip: write the limitation of direct sources.

Correct answer: A. Physical properties of the medium are different

Wave speed depends on properties like density and elasticity. Exam tip: infer material property from wave speed.

Correct answer: A. In upper mantle below lithosphere

Asthenosphere is the weak part of upper mantle below lithosphere. Exam tip: focus on layer position.

Correct answer: A. How seismic waves change at different depths

Changes in seismic waves give information about internal layers. Exam tip: choose seismic data for scientific evidence.

Correct answer: A. Crust least dense and core most dense

Density generally increases from surface toward centre. Exam tip: remember density order from crust to core.

Correct answer: A. Classification by mechanical properties

Mesosphere is linked with lower mantle in mechanical layering. Exam tip: keep mesosphere with lower mantle.

Correct answer: A. SIAL is associated with silica- and aluminium-rich lighter crustal materials, whereas the core is associated with NIFE

SIAL is derived from silica (Si) and aluminium (Al), and it is associated mainly with the relatively lighter materials of the continental crust. In contrast, the core is called NIFE because nickel (Ni) and iron (Fe) are its major constituents. Therefore, calling the core SIAL is incorrect. Exam tip: remember SIAL for the crust and NIFE for the core.

Correct answer: A. Sudden change in speed and direction of seismic waves

At a discontinuity material changes so wave behaviour may suddenly change. Exam tip: identify discontinuity by sudden wave change.

Correct answer: A. Use of both direct samples and geophysical indirect evidence

Direct sources are limited so study with indirect evidence is necessary. Exam tip: remember combined evidence approach.

Correct answer: A. Temperature pressure and state of material

Core has very high temperature and pressure but pressure keeps inner core solid. Exam tip: remember temperature pressure balance.

Correct answer: B. Drilling sample direct source

A drilling sample is directly obtained from Earth so it is a direct source. Exam tip: place samples under direct source.

Correct answer: A. Outer core liquid and related to magnetic field

Outer core is a liquid metallic layer linked with geomagnetic field. Exam tip: remember two clues for outer core liquid and magnetism.

Correct answer: A. It is wrong because mantle is the thickest major layer

Mantle is a very extensive layer between crust and core. Exam tip: remember mantle as the thickest major layer.

Correct answer: B. Production of internal heat

Radioactive decay is one source of Earth's internal heat. Exam tip: remember radioactive decay under internal heat sources.

Correct answer: C. Increase of temperature with depth

Geothermal gradient shows increase in temperature with depth. Exam tip: connect geothermal gradient with depth temperature relation.