$\frac{{\mathrm{t}}_{75\%}}{{\mathrm{t}}_{50\%}}$ of a first order reaction is T₁. $\frac{{\mathrm{t}}_{75\%}}{{\mathrm{t}}_{50\%}}$  of a zero reaction is T₂. 

T₁ : T₂ is equal to

$$\begin{gathered} \left(\mathrm{I}\right) \mathrm{First} \mathrm{order} \\ \frac{{\mathrm{t}}_{75\%}}{{\mathrm{t}}_{50\%}}=2 ---- {\mathrm{T}}_1 ; \\ \left(\mathrm{II}\right) \mathrm{Zero} \mathrm{order} \\ \mathrm{x}=\mathrm{Kt} \\ \frac{{\mathrm{t}}_1}{{\mathrm{t}}_2}=\frac{{\mathrm{x}}_1}{{\mathrm{x}}_2} \\ \frac{{\mathrm{t}}_{75\%}}{{\mathrm{t}}_{50\%}}=\frac{75}{50}=\frac{3}{2} ---- {\mathrm{T}}_2 ; \\ {\mathrm{T}}_1 : {\mathrm{T}}_2 =2 : \frac{3}{2} ; \\ {\mathrm{T}}_1 : {\mathrm{T}}_2 =4 : 3 ; \end{gathered}$$