$a/$
$4P +5O_{2}→ 2P_{2}O_{5}$
$b/$
$nP=6,2/31=0,2mol$
$theo$ $pt:$
$nO2=5/4.nP=5/4.0,2=0,25mol$
$⇔V_{O_{2}}=0,25.22,4=5,6l$
$c/pthh :$
$2KClO3→2KCl + 3O2$
$V_{O_{2}}=5,6.85\%=4,76l$
$⇒n_{O_{2}}=4,76/22,4=0,2125mol$
$theo$ $pt:$
$nKClO3=2/3nO2=2/3.0,2125=0,14mol$
$⇒mKClO_{3}=0,14.122,5=17,15(g)$