Cho các phản ứng hoa học sau: (a) HCl + KOH -> KCl +H2C

Cho các phản ứng hoa học sau:

(a) $HCl + KOH \to KCl + H_{2}C$.

(b) $2\text{H}\text{C}\text{l}+\text{N}{\text{a}}_2\text{C}{\text{O}}_3\to 2\text{N}\text{a}\text{C}\text{l}+\text{C}{\text{O}}_2+{\text{H}}_2\text{O}$.

(c) $2\text{H}\text{C}\text{l}+\text{F}\text{e}\to \text{F}\text{e}\text{C}{\text{l}}_2+{\text{H}}_2$.

(d) $4\text{H}\text{C}\text{l}+\text{M}\text{n}{\text{O}}_2\to \text{M}\text{n}\text{C}{\text{l}}_2+\text{C}{\text{l}}_2+2{\text{H}}_2\text{O}$.

Số phản ứng oxi hoá - khử là