$200ml$ of pure oxygen is subjected to electric discharge, $15\%$ of oxygen is converted into ozone. The volume of ozonized oxygen is

The balanced chemical reaction is as follows:

$1.5O_2\to O_3$

We can find $15\%$ of $200ml$ :

$\frac{200\times 15}{100}=30ml$

From the balanced chemical reaction:

$30ml$ of $O_2$ will give $\frac{30}{1.5}ml$ of $O_3$ $=20ml$ of $O_3$

170ml of oxygen left and 20 ml of ozone formed, so total volume of ozonized oxygen will be 190ml