in case of parallel plate capacitor which i have considered here the Da=q

where D : flux density

a: surface area

q: total charge on one plate

and we also know that surface charge density is defined as :

charge density is a measure of electric charge per unit volume of space, in one, two or three dimensions. More specifically: the linear, surface, or volume charge density is the amount of electric charge per unit length, surface area, or volume, respectively. The respective SI units are C·m−1, C·m−2 or C·m−3

from:

http://en.wikipedia.org/wiki/Charge_density
so here in case of parallel plate capacitor we have charge density σ=q/a ( surface charge density charge per unit area)

and we also have the relation bet flux density D with E electric field intensity D=εE

and E=σ/ε ( one can find this from gauss law for parallel plate capacitors)

so both D and σ are here equal and

but we know that charge density is definitely

**NOT** a vector but flux density is a vector so both being equal in magnitude one has defined as scalar and other as vector..??