$n_{H_2}=11,2/22,4=0,5mol$
$PTHH :$
$2H_2+O_2\overset{t^o}{\longrightarrow}2H_2O$
$ a/$
Theo pt :
$n_{H_2O}=n_{H_2}=0,5mol$
$⇒m_{H_2O}=0,5.18=9g$
$b/$
Theo pt :
$n_{O_2}=1/2.n_{H_2}=1/2.0,5=0,25mol$
$⇒m_{O_2}=0,25.32=8g$
$c/$
$2KMnO_4\overset{t^o}{\longrightarrow}K_2MnO_4+MnO_2+O_2$
Theo pt :
$n_{KMnO_4}=2.n_{O_2}=2.0,25=0,5mol$
$⇒m_{KMnO_4}=0,5.158=79g$