Elastic behaviour of solids - class-XI

More elastic means, the value of an elastic constant is more and. Steel have move elastic constant in compare to Rubber, So Steel is more elastic than rubber.
All other statements are correct.

For most of the materials, elasticity decreases with temperature. One exception is invar steel.

Whenever a deforming force is applied to a non-rigid substance, the substance undergoes deformation in dimension or shape. Elastic substances are those which come back to their original shape or dimensions after the deformation force is removed. Plastic substances are those which do not come back to their original shape or dimensions even after the deformation force is removed.

Whenever a deforming force is applied to a non-rigid substance, the substance undergoes deformation in dimension or shape. Plastic substances are those which do not come back to their original shape or dimensions even after the deformation force is removed.
Substances like clay, putty, mud etc., are highly plastic in nature

According to Hooke's law, within elastic limit,

Compressive strength is the capacity of a material or structure to withstand loads tending to reduce size, as opposed to tensile strength, which withstands loads tending to elongate.

The property of a body to regain its original shape when the deforming force is removed from it or to oppose the change in its original shape is called elasticity.

Elasticity is defined as the ability of a body to  resist a distorting influence and to return to its original size and shape when that influence or force is removed.

Substances that elongate considerably and undergo plastic deformation before they break are known as ductile substances

Two prominent mechanisms of plastic deformation, namely slip and twinning occur . 
1. Slip involves sliding of blocks of crystal over one other along definite crystallographic planes, called slip planes. During slip each atom usually moves same integral number of atomic distances along the slip plane producing a step, but the orientation of the crystal remains the same.

2. Portion of crystal takes up an orientation that is related to the orientation of the rest of the untwined lattice in a definite, symmetrical way. The twinned portion of the crystal is a mirror image of the parent crystal.

Substances that break just after elastic limit is reached are known as brittle substances

The yield point is the point on a stressstrain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers.

The correct option is option(a)

Plasticity is defined as the property which enables a material to be deformed continuously and permanently without rupture during the application of force. This deformation determines the viscous behavior of the material and is irrecoverable.

Beyond the elastic limit, permanent deformation will occur. The elastic limit is therefore the lowest stress point at which permanent deformation can be measured. At yield point, permanent deformation occurs or the substance becomes plastic.

The correct option is option (b)

The yield point is the point on a stressstrain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers.

Thus, Hooke's law dosent hold good in this region, as stress is not proportional to strain in this region

A perfectly plastic body is one that undergoes permanent deformation under stress and does not recover its original shape when the deforming force is removed. Plasticine is a non-drying clay that exhibits near-perfect plasticity.

An elastic rod changes its length when subjected to a tensile force (being pulled). Falling vertically under its own weight also causes stress and potential elongation, but pulling is the standard demonstration of elastic deformation.

When a material is stressed beyond its elastic limit, it does not return to its initial dimensions upon unloading, retaining a permanent strain or deformation known as a set.

Modulus of elasticity gives the idea of elasticity. For above materials, values of E are:
Glass: $50-90 GPa$
Rubber:$ 0.01-0.1 GPa$
Steel:$ 200 GPa$
Copper: $117 GPa$

Crystals are typically anisotropic, meaning their physical properties (like thermal expansion) vary depending on the direction of measurement. Many crystals exhibit this property.

Putty is widely used as a standard textbook example of a body that exhibits very little elasticity and behaves almost as a perfectly plastic material when subjected to forces.

Elastic materials are those that follow the Hooke's law, which is that the deformation produced in a material is directly proportional to the stress applied to it, and the material is recoverable after the deformation force is removed.