\(n_{SO_2}=\dfrac{7.84}{22.4}=0.07\left(mol\right)\)
\(2SO_2+O_2\underrightarrow{^{t^0}}2SO_3\)
\(0.07.............0.07\)
\(m_{dd_{H_2SO_4}}=57.2\cdot1.5=85.8\left(g\right)\)
\(m_{H_2SO_4}=85.8\cdot60\%=51.48\left(g\right)\)
\(SO_3+H_2O\rightarrow H_2SO_4\)
\(0.07..................0.07\)
\(m_{dd}=0.07\cdot80+85.8=91.4\left(g\right)\)
\(\sum n_{H_2SO_4}=0.07\cdot98+51.48=58.34\left(g\right)\)
\(C\%_{H_2SO_4}=\dfrac{58.34}{91.4}\cdot100\%=63.8\%\)