Selecting a material always means matching mechanical properties to the service conditions. Here the component sees two demanding conditions simultaneously: cyclic (repeated) loading, which promotes fatigue crack initiation and growth, and impact (shock) loading, which applies energy suddenly.

The two key properties for such a duty are:

• Hardness — resistance to surface wear, indentation and abrasion. It protects the working surface but says nothing about how the bulk material behaves when it is suddenly overloaded.
• Toughness — the ability to absorb energy and deform plastically before fracturing. It is essentially the area under the stress–strain curve. High toughness lets the part survive shock loads and blunts the tips of fatigue cracks, resisting sudden brittle failure.

A material that is hard but not tough (i.e., hard and brittle, like fully hardened untempered steel) may resist wear yet shatter under a single impact or crack under repeated stress. That is why, alongside hardness, toughness must be considered to resist sudden failure. In practice this trade-off is managed by processes such as tempering or case-hardening, giving a hard surface over a tough core.

Why the other choices are wrong: the statement that plasticity must be considered to increase mass is meaningless — plasticity is the tendency to deform permanently and has nothing to do with adding mass. Ductility to avoid oxidation confuses a mechanical property with corrosion resistance; oxidation is governed by chemistry/coatings, not ductility. Elasticity for better insulation is also unrelated — elasticity concerns recoverable deformation, while insulation is a thermal/electrical property.