Use the electron-transfer method to balance this equation:

Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)

a. 2Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)

b. Zn(s) + 2HCl(aq) →ZnCl2(aq) + H2(g)

c. Zn(s) + HCl(aq) →ZnCl2(aq) + H2(g)

d. 2Zn(s) + 4HCl(aq) → 2ZnCl2(aq) + 2H2(g)

e. 3Zn(s) + 3HCl(aq) →3ZnCl2(aq) + 3H2(g)

The answer to your question is the letter d.

Explanation:

Data

                Zn  +  HCl   ⇒  ZnCl₂  +  H₂

- Calculate the Oxidation number of reactants and products

              Zn⁰  +  H⁺¹Cl⁻¹   ⇒  Zn⁺²Cl₂⁻¹  +  H₂⁰

- Determine which elements changed their oxidation numbers

                      Zn⁰     ⇒   Zn⁺²                Zn lost 2e⁻

                     2H⁺¹      ⇒   H₂⁰                H won 2 e⁻

-Interchange the electrons lost and won

                  2( Zn⁰     ⇒   Zn⁺²)

                  2(2H⁺¹      ⇒   H₂⁰)

-Simplify

                  2Zn⁰     ⇒   2Zn⁺²

                  4H⁺¹      ⇒   2H₂⁰

-Substitute the coefficient in the equation

                2Zn  +  4HCl   ⇒  2ZnCl₂  +  2H₂  

             Reactant       Element      Product

                  2                    Zn                2

                  4                     H                 4

                  4                     Cl                 4

- Now the reaction is balanced

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.