The SI of force is :
(a) Torr
(b) Newton
(c) Joule
(d) Dyne

Hint: In this question use the relation between force, mass and acceleration.We know that that force is ${\text{mass}} \times {\text{acceleration}}$. Using this relation we get the required S.I unit of force.

Complete step-by-step answer:
As we know one newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.
In more formal terms, Newton's second law of motion states that the force exerted by an object is the multiplication of the acceleration and mass of that object, namely:
F = ma.
A force has both magnitude and direction, making it a vector quantity.It is measured in the SI unit of newtons and represented by the symbol F. And it is first discovered by scientist Isaac Newton so the S.I unit of force is named on him which is Newton.
So the S.I unit of force is Newton.
Hence option (B) is correct.

Note : SI units is known as international systems of units, it is a system of physical units based upon the meter, kilogram, second, ampere, kelvin, candela and mole together with a set of prefixes to indicate the multiplication or division by a power of 10. In C.G.S system absolute unit of force is Dyne (dyn). The relation between newton and dyne is $1N=10^5dyne$