# $2SO_2+O_2+x\rightarrow 2H_2SO_4$.The $x$ is

$\begin{array}{1 1}(a)\;H_2O\\(b)\;H_3O\\(c)\;2H_2O\\(d)\;O_2\end{array}$

$2SO_2+O_2+2H_2O\rightarrow 2H_2SO_4$
Hence x is $2H_2O$
Hence (b) is the correct answer.