In a four-stroke internal combustion engine:
One complete thermodynamic cycle (Suction, Compression, Power, Exhaust) requires 4 strokes of the piston and 2 complete revolutions of the crankshaft (720°).
During this cycle, each valve (inlet and exhaust) opens exactly once.

Kinematics of slider-crank mechanism in IC engines:
The piston velocity is given by: \(v = r \omega \left(\sin\theta + \frac{\sin 2\theta}{2n}\right)\).

• At Top Dead Centre (\(\theta = 0^\circ\)) and Bottom Dead Centre (\(\theta = 180^\circ\)), \(\sin\theta = 0\), so piston velocity is strictly ZERO (it momentarily stops to reverse direction). Velocity is maximum near the middle of the stroke (\(\theta \approx 75^\circ - 90^\circ\)). Thus, Statement (I) is false.

The piston acceleration is given by: \(a = r \omega^2 \left(\cos\theta + \frac{\cos 2\theta}{n}\right)\).

• Acceleration reaches its maximum absolute values at the dead centers (\(\theta = 0^\circ\) at TDC and \(\theta = 180^\circ\) at BDC) where the direction of motion reverses. Thus, Statement (II) is true.