Active mass of 1 gram of hydrogen at STP is X.  Active mass of 10 grams of limestone in 10 litre vessel is Y.  Y : X is 

$n_{CaC{O}_3}=\frac{10}{100}=0.1$=

For solid $CaC{O}_3$ , active mass is one.
Number of moles of $H_2=\frac{1}{2}=0.5$ 
Active mass $=\frac{0.5}{11.2}=\frac{1}{22.4}$  
$X:Y=\frac{1}{22.4}:1=1:22.4$