Refer to the below equation :

Question

From the equation given above the formulae for Borax Glass is

$\begin{array}{1 1}(a)\;2NaBO_2\\(b)\;2NaBO_2+B_2O_3\\(c)\;NaBO_2+B_2O_3\\(d)\;4Na_2BO_2+B_2O_3\end{array}$