Why do the reactants zinc and hcl(hydrochloric acid) indicate the reaction of single displacement?

 the reactant Zinc and HCl  indicate  the single  displacement  because

zinc  metal displaces  hydrogen from HCl to form   hydrogen  gas and  zinc chloride.

Explanation

A  single  displacement   reaction is type of reaction in which element  react  with  compound  and take the place of another  element  in that compound.

When Zn  react  with HCl ,  Zn (an element)  displaces H  from Hcl (compound) to  H₂ gas  and ZnCl₂ according to equation  below

Zn  +2 HCl→ znCl₂  +H₂

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.