(a) Define mass of a body. What is the SI unit of mass?
(b) Define weight of a body. What is the SI unit of weight?
(c) What is the relation between mass and weight of a body?

(a). Mass: The mass of an object is the quantity of the matter in it. The SI unit of mass is $kg$.

(b). Weight: The weight of an object is the gravitational force on the object to attract it towards the center of the earth is called its weight. The SI unit of weight is $N$.

(c). Relationship between the mass and the weight of the object:

$\boxed{W=mg}$

Here, $W\rightarrow$Weight of the body

$m\rightarrow$ mass of the object

$g\rightarrow$ gravitational acceleration