Material comparison: compared to polyethylene (polythene), polypropylene is generally…

Introduction / Context:
Polypropylene (PP) and polyethylene (PE) are closely related polyolefins, but their properties differ due to methyl side groups in PP, which increase stiffness and reduce density. This question checks qualitative property trends designers rely on when choosing between PP and PE.

Given Data / Assumptions:

• Commodity grades compared at ambient conditions.
• PE reference is LDPE/HDPE range; PP is isotactic, unfilled.
• Density, stiffness, and strength are considered.

Concept / Approach:
The methyl group on every other carbon in PP restricts chain mobility and increases crystallinity effects, yielding higher modulus and tensile strength than LDPE and many HDPE grades, while maintaining a lower density (~0.90–0.91 g/cm^3) than PE (~0.92–0.96 g/cm^3). Thus, PP is typically lighter, harder (stiffer), and stronger in many applications.

Step-by-Step Solution:
Evaluate density: PP < PE → lighter.Assess stiffness/strength: PP > LDPE and competitive with HDPE → harder/stronger.Select 'All (a), (b) and (c)' as the best summary.

Verification / Alternative check:
Datasheets: PP density ~0.90 g/cm^3; HDPE ~0.95 g/cm^3; modulus and tensile values for PP exceed LDPE and often rival HDPE, confirming the trend.

Why Other Options Are Wrong:
Single-trait options are incomplete; all three traits are usually observed.

Common Pitfalls:
Assuming 'hardness' as scratch resistance; here, 'harder' refers to stiffness/modulus—a conventional shorthand in basic MCQs.

Final Answer:
All (a), (b) and (c)