A single-displacement reaction, likewise named single-substitution response, is a sort of oxidation-decrease synthetic response when a component or particle moves out of one compound and into another - that is, one component is supplanted by another in a compound.

A solitary removal response happens when a component replaces another component in a compound. A metal just replaces a metal, and a nonmetal just replaces a nonmetal. Just a more responsive component can supplant the other component in the compound with which it responds.

With a solitary substitution simply take the two metals ans switch them based of reactivity arrangement. for this situation Zn is higher up on the reactivity arrangement than hydrogen, so Zn and H will switch spotes

Zn and HCl

Zn+2HCl - > H2 + ZnCl2

Keep in mind that H is a diatomic so when its without anyone else's input it will have a subscript of 2 and that causes you to change the coefficient of the reactants HCl. what's more, now that we have the coefficients of Hcl we know which charge of Zn to utilize, either the 2+ or 4+. Since the coefficient of HCl is 2 that meants that there must be 2 Cl's on the item side so the charge of Zn must be 2+.

Again your last response is

Zn + 2HCl - > H2 + ZnCl2