# There are as many notes as number of oxygen atoms in 24.8g $Na_2S_2O_3.5H_2O$ (molecular weight =$248gmol^{-1})$.A note-counting machine counts 48 million notes per day.Days taken to count these notes are
$\begin{array}{1 1}(a)\;10^{17}& (b)\;10^{16} \\(c)\;10^{10} &(d)\;10^{12}\end{array}$