In the equation $\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\to 2{\mathrm{CaCO}}_3+2{\mathrm{H}}_2\mathrm{O}$ The F-number 2 for

Definition: “ The frequency of occurrence of various elements in an equation is called F number”

$\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\to 2{\mathrm{CaCO}}_3+2{\mathrm{H}}_2\mathrm{O}$

In the above equation, the element carbon, C has F-number 2