Correct gas equation is :

If temperature, volume and pressure of fixed amount (say n mole) of a gas vary from $T_1,V_1\text{and}{p}_1\text{ to }{T}_2.V_2$ and $p_2$ respectively. Then, ideal gas equation for two states can be written as
$p_1{V}_1=nR{T}_1$
$\text{or }\frac{p_1{V}_1}{T_1}=nR\text{ ...(i)}$
$p_2{V}_2=nR{T}_2$
$\text{or }\frac{p_2{V}_2}{T_2}=nR\text{ ...(ii)}$
On combining Eqs. (i) and (ii), we get
$\frac{p_1{V}_1}{T_1}=\frac{p_2{V}_2}{T_2}$
$\text{or }\frac{p_1{V}_1}{p_2{V}_2}=\frac{T_1}{T_2}$
So, it called combined gas equation.
Hence, (c) answer is correct.