Question

give the definition of resistivity and write formula for it

Answer 1

RESISTIVITY:  
definition is
 "it is equal to the resistance of a conductor of unit length and unit area of cross section"
                  formula for resistivity is
ρ=$\frac{RA}{l}$
here R is resistance of conductor
A is the area of cross section
l is length

Answer 2

resistivity known as the power or capacity of material to resist electricity to pass in unit area. 
Formula for that is ρ = RA                                                             
                                     l
R is the electrical resistance mesure in Ω [ohm]
A is the croos section area of materia 
l is the length of the piece of material