`NH_(4)Cl(s)` is heated in test tube.Vapours are brought in contract with red litmus paper, which changes to blue and then to red.It is because of :
A. Formation of `NH_(3),H_(2)O and HCl`
B. Formation of phosphorici acid
C. greater diffusion of `NH_(3)` than `HCl`
D. greater diffusion of HCl than `NH_(3)`
