Before equilibrium is set-up the chemical reaction `N_(2)O_(4)(g) hArr 2NO_(2)(g)`, vapour density d of the gaseous mixture was measured. If D is the theoretica value of vapour density, variation of `alpha` with `D//d` is given by the graph below. What is value `D//d` at point A` ?
A. 1
B. 0.5
C. 1
D. 1.5