The empirical formula of oxalic acid $\left({\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4\right) is$

The simplest ratio of the no of atoms of different element of a compound Gives empirical formula. Molecular formula $={\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4$

Reduce the M.F Divide the subscripts of oxalic acid by the greatest common factor.

Oxalic acid (GCF) = 2

$\frac{2}{2}\frac{2}{2}\frac{4}{2}=1,1,2$

Empirical formula of oxalic acid =${\mathrm{HCO}}_2$