\(n_{C_2H_2}=\dfrac{2.6}{26}=0.1\left(mol\right)\)
\(n_{CH_4}=\dfrac{7.6}{16}=0.475\left(mol\right)\)
\(C_2H_2+\dfrac{5}{2}O_2\underrightarrow{t^0}2CO_2+H_2O\)
\(CH_4+2O_2\underrightarrow{t^0}CO_2+2H_2O\)
\(m_{O_2}=\left(\dfrac{5}{2}\cdot0.1+0.475\cdot2\right)\cdot32=38.4\left(g\right)\)