The product of the moment of inertia and the angular acceleration is:

CONCEPT:

Torque (τ): 

• It is the twisting force that tends to cause rotation.
• The point where the object rotates is known as the axis of rotation. 
• Mathematically it is written as,

τ = rFsin θ 

• Angular acceleration (α): It is defined as the time rate of change of angular velocity of a particle is called its angular acceleration.
• If Δω is the change in angular velocity time Δt, then average acceleration is

EXPLANATION:

• Torque is the measure of the amount of force acting on an object that can cause it to rotate.
• The torque that is needed to produce angular acceleration depends on the mass distribution of the object which is described by the moment of inertia.
• Therefore, torque () is the product of the angular acceleration (a) and the moment of inertia (I) of an object. Therefore option 2 is correct.