[Karch]

Not sure why this is so difficult.

The OP got the test answer incorrect, because an engine's torque peak occurs when it reaches maximum volumetric efficiency, or, in layman's terms, when it best fills the cylinder.

There are a lot of variables that go into this, but the most common ones are rod/stroke ratio, bore/stroke ratio, CAM TIMING (caps because it includes duration, LSA, ramp rates, valve closing timing, etc), cylinder head design (port and chamber), exhaust system, from the heads on back, as this tweaks the scaveging, thereby altering VE, etc.

Also, tuning may alter the peak torque realized as well as rpm at which it occurs, but if tuned properly, the tune itself will not alter the peak torque rpm.

Torque, in engineering terms, is a force acting through a rotation, where force (F) is equal to a mass times acceleration.

Weight is a force, mass is not, thus pounds (SAE) is a force, and kilograms is not. Gravity is not a force, it's acceleration.