Question

Why is the active mass of water is 55.5 ?

Answer 1

Active mass is basically Molar cone or No. of moles per litre.

$\begin{array}{cc}For{H}_{2}O\to 1Lsample& Densityis1g/ml\\ Somassof{H}_{2}O=1000g& \\ Activemass=\frac{1000}{\frac{18}{1L}}\Rightarrow 55.5& \\ Activemass=55.5& \end{array}$