Assertion–Reason on amorphous solids formation Assertion (A): An amorphous material is obtained when atomic mobility is strongly inhibited during solidification (e.g., rapid quenching). Reason (R): For most solids, the crystalline state is the natural equilibrium state.

Introduction / Context:
Whether a solid becomes crystalline or amorphous depends on atom mobility during solidification and the thermodynamic driving force toward order. This item checks understanding of kinetic inhibition (glass formation) versus thermodynamic preference (crystallinity).

Given Data / Assumptions:

• Cooling from melt or vapor to a solid phase.
• “Amorphous” means lacking long-range periodic order (glass-like).
• Most crystalline solids have a lower Gibbs free energy than the corresponding amorphous phase at standard conditions.

Concept / Approach:
Crystallization requires atoms to diffuse to lattice positions and nucleate ordered regions. If cooling is very fast or viscosity rises quickly, diffusion is arrested; atoms cannot reach equilibrium lattice sites and the structure “freezes in” as amorphous. Thus inhibiting mobility is a practical route to amorphous materials (metallic glasses, silicate glasses). The reason correctly states the thermodynamic backdrop: crystalline order is typically the equilibrium state; amorphous formation is therefore a kinetic phenomenon.

Step-by-Step Solution:
Recognize that crystallization needs nucleation + diffusion.Fast quench or increased viscosity limits atomic mobility.Kinetic arrest prevents reaching the crystalline minimum → amorphous solid results.Since crystals are thermodynamically favored, only strong kinetic inhibition yields amorphous phases.

Verification / Alternative check:
Glass transition in silica and metallic glasses formed by rapid quenching corroborate the mobility–structure link: higher cooling rates promote amorphous structure; slower cooling allows crystallization.

Why Other Options Are Wrong:
Claiming R does not explain A ignores the kinetic-versus-thermodynamics narrative. Saying A or R is false contradicts well-established materials science.

Common Pitfalls:

• Confusing metastability (amorphous) with stability (crystalline) at equilibrium.
• Assuming any high cooling rate guarantees amorphous structure; critical rates vary with composition.

Final Answer:
Both A and R are true and R is correct explanation of A